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April 25, 2019, 16:44:21 PM

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Author Topic: It's a talking point. 737 Max series.  (Read 1927 times)

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Offline SteveBB

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It's a talking point. 737 Max series.
« on: April 07, 2019, 16:13:17 PM »

I hope that things can be resolved and these avoidable tragedies don't happen again,  Will Hutton has an interesting piece about it, and just how compromised the FAA is. I think though that Boeing are too big to fail or even realistically be held accountable. What can happen to them? The people who signed it off might not even work there anymore.  :-\


https://www.theguardian.com/commentisfree/2019/apr/07/boeing-737-max-regulation-corporate-america
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Offline itsme

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Re: It's a talking point. 737 Max series.
« Reply #1 on: April 07, 2019, 18:09:46 PM »
The whole automation thing needs to be addressed. I thought they would learn that there are times that a human has to take over after the Paris Air Show accident. Whats wrong with a big MANUAL switch? Can't pilots fly any more?

Offline PDR

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Re: It's a talking point. 737 Max series.
« Reply #2 on: April 07, 2019, 18:52:49 PM »
It's not about automation - it's about commercial pressure to find cheaper ways through the certification requirements.

this article seems to have a reasonable handle on it ( apart from the author's fixation with the term "high speed stall" when he just means "stall" - they are different things and he clearly doesn't mean the former). If the allegations are accurate then I struggle to see how Boeing could continue to hold its Design Authority approval (other than the "too big to fail" thing). I summarised my thoughts in an internal communication a few days ago as:

Quote from:  "Me"
My only thought would be that I think I can genuinely say that some of the critical contributors couldn’t happen here. Specifically:

•   Overdue safety analyses being issued before completion under a senior management (rather than Engineering) signature
•   Any flight-control subsystem being dependant on one sensor (at all) let alone with no “test of reasonableness” or kalman filtering
•   That amount of control authority being given to a subsystem that had a lower safety criticality classification

I’m also fairly sure we wouldn’t have accidentally allowed maximum control authorities for successive events to become cumulative. But the thread about the unaffordable cost of adequate regulation/governance certainly strikes the odd chord.

PDR
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Offline SteveBB

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Re: It's a talking point. 737 Max series.
« Reply #3 on: April 08, 2019, 02:05:53 AM »
It's not about automation - it's about commercial pressure to find cheaper ways through the certification requirements.

this article seems to have a reasonable handle on it ( apart from the author's fixation with the term "high speed stall" when he just means "stall" - they are different things and he clearly doesn't mean the former). If the allegations are accurate then I struggle to see how Boeing could continue to hold its Design Authority approval (other than the "too big to fail" thing). I summarised my thoughts in an internal communication a few days ago as:

PDR

 Could/would the airlines and indeed other aircraft manufacturers demand that Boeing have their Design Authority approval revoked until such time as they earn it back but this time on condition that the FAA doesn't allow Boeing to certify itself? That the FAA has been robbed of funding isn't the problem of other manufacturers but could be the catalyst for the FAA to regain it's independence, no?
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Offline itsme

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Re: It's a talking point. 737 Max series.
« Reply #4 on: April 08, 2019, 08:08:19 AM »
I have heard that the aircraft has C of G problems with the size/weight of the engines- designed for maximum efficiency- and the system was a 'fix' for an unstable aircraft. Any truth in that? Also that without those aircraft flying, reverting to older, less efficient models will bankrupt a number of airlines who had costed flights based on the excellent fuel savings?


Offline meharibear

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Re: It's a talking point. 737 Max series.
« Reply #5 on: April 08, 2019, 10:02:07 AM »
I have heard that the aircraft has C of G problems with the size/weight of the engines- designed for maximum efficiency- and the system was a 'fix' for an unstable aircraft. Any truth in that? Also that without those aircraft flying, reverting to older, less efficient models will bankrupt a number of airlines who had costed flights based on the excellent fuel savings?
Similarly I read that the engine thrust-lines are all wrong as they raised the intake to keep it clear of runway debris resulting in considerable up-thrust.  Certainly. looking at the aircraft that seems to be the case, and, as aeromodellers we don't need to be told that a thrust line significantly lower than the drag line needs down-thrust not up thrust!  Hence opening the throttle results in huge adverse trim changes which are kept in check by not so cunning software.
Inside every old person is a young person wondering what happened.  (Terry Pratchett)

Offline flynn

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Re: It's a talking point. 737 Max series.
« Reply #6 on: April 08, 2019, 10:41:49 AM »
I have found reading the https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa-113.html thread quite enightening. PPrune is a professional pilots forum, although you do get quite a few other, normally related, professionals on there too, and thankfully only a very few en-enlightened types like us posting.....get comfy if you want to read it from the start though......


Offline PDR

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Re: It's a talking point. 737 Max series.
« Reply #7 on: April 08, 2019, 12:48:27 PM »
I have heard that the aircraft has C of G problems with the size/weight of the engines- designed for maximum efficiency- and the system was a 'fix' for an unstable aircraft. Any truth in that?

No. The issue is that there are a set of certification requirements around stickforce gradient (both stickforce-per-G and stickforce-per-alpha) which require that the stickforce required to achieve higher alpha (and G) must always increase by at least minimum amount per degree of alpha at all speeds and in all configurations. The higher thrustline and greater low-speed thrust of the 737Max's engines made this difficult to achieve aerodynamically (it would have needed changes to tailplane shape & gearing, which would have cost megabucks to do). So they came up with an alternative approach of adding the kickdown system.

Now if it had been a "stick pusher" system it would have been fine, but as that is a change to a primary flight control it would have cost a lot to design and certify. But by making it "separate" they came up with an argument that claimed it WASN'T a primary flight control (as per the article I linked to earlier), so it was simpler/quicker/cheaper to implement. Ironically according to the data I have available to me in-service the kickdown system has only actually been triggered twice - both times tent-pegging the aeroplane.

Quote
Also that without those aircraft flying, reverting to older, less efficient models will bankrupt a number of airlines who had costed flights based on the excellent fuel savings?

Perhaps, but they will have been purchased with contractual dispatch availability guarrantees (all airliners are sold that way these days), so unless Boeing actually go bust then ultimately they will be footing the whole bill for everyone. Of course the whole bill is likely to be a very large chunk of change (even by Wiz's standards), so it's by no means certain that Boeing WON'T go bust under the load.

€25,000 supplied (e&oe),

PDR
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Offline itsme

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Re: It's a talking point. 737 Max series.
« Reply #8 on: April 08, 2019, 15:10:57 PM »
Whatever happens, its going to impact aviation, with a lot of trust in airliners (especially Boeing) lost. We dont expect the safety technology to kill us. It somehow feels safer to put our trust in a (fallible) human pilot. And from what you say, it seems to my laymans way of thinking that it IS a fix for an unstable aeroplane. Flying is so safe nowadays that this event and the other (s) are so shocking. Who (after the inevitable fix) will be totally happy climbing aboard one of these aircraft?


Offline SteveBB

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Re: It's a talking point. 737 Max series.
« Reply #9 on: April 08, 2019, 15:29:26 PM »
Whatever happens, its going to impact aviation, with a lot of trust in airliners (especially Boeing) lost. We dont expect the safety technology to kill us. It somehow feels safer to put our trust in a (fallible) human pilot. And from what you say, it seems to my laymans way of thinking that it IS a fix for an unstable aeroplane. Flying is so safe nowadays that this event and the other (s) are so shocking. Who (after the inevitable fix) will be totally happy climbing aboard one of these aircraft?
[/b]

As I read someone else say, make the Boeing execs and US officials take the first two hundred test flights.
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Offline PDR

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Re: It's a talking point. 737 Max series.
« Reply #10 on: April 08, 2019, 15:51:01 PM »
Whatever happens, its going to impact aviation, with a lot of trust in airliners (especially Boeing) lost. We dont expect the safety technology to kill us. It somehow feels safer to put our trust in a (fallible) human pilot.

...which is (of course) completely irrational. If you add up the crashes due to pilot error and the crashes due to technology failures you find the former massively outnumber the latter. The trick is not to get grabbed by the headlines.

Quote
And from what you say, it seems to my laymans way of thinking that it IS a fix for an unstable aeroplane.

No, it definitely isn't. It was a fix for handling feel that didn't meet the regs - the aeroplane wasn't (and isn't) "unstable" by any rational definition of the word. That would be like calling trimwheels a " fix for an unstable aeroplane", but we've had them in aeroplanes for over a hundred years. Unfortunately this is one of those aspects where model-flying experience gives a false perception of issues in full-size aviation. Firstly because model aeroplanes have no "handling feel" - the sticks have simple springs which give the same feel regardless of airspeed and AoA.

But secondly it's because models (even very large ones) have only instantaneous control responses. Full size aeroplanes have the short-term "transient" control response *and* the steady-state control response. The two are different, and the relationship between the two changes massively depending on airspeed, altitude and AoA (to name but three - you could also include current weight and several other parametrs).

Airliners are wallowy beasts and their controls only really "influence" rather than "direct" the aeroplane. Pilots have to be a long way ahead of the aeroplane to avoid problems. The3re are airliners which, once they have started pitching up, cannot avoid stalling even if the driver applies full forward stick 10 seconds before the stall happens. This isn't being "unstable" - it's just showing the effect of the inertia of a couple of hundred tons of aeroplane and fuel. That's why they have to be established on a 10-mile stabilised approach to have any hope of hitting the runway at anything close to the right speed (horizontal and vertical) while pointing in the right direction. Picture trying to park a fully-loaded bus in a parking bay on an ice-rink while having a minimum speed of 160mph for all but the last 30 yards - it's a bit like that only harder.

So it's not just a matter of giving biggles direct control of the ailerons and elevators - he'd just make a smoking hol;e in the landscape 3 times out of four. It's much, much more involved than that.

PDR
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Offline itsme

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Re: It's a talking point. 737 Max series.
« Reply #11 on: April 08, 2019, 19:35:52 PM »
I agree its irrational- but thats what will happen. I understand the 'oil tanker' principal of planning miles ahead, but most passengers will not grasp that - when you think about it, you really dont want to fly in one! It may be the safest form of travel, but climbing out of cloud with the thing shaking with turbulence it doesnt feel like it is...its at that point I always feel unnerved.

Offline Bad Raven

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Re: It's a talking point. 737 Max series.
« Reply #12 on: April 09, 2019, 12:45:40 PM »
From what I have read, if correct, the almost "transparent to crew" system, tied back to a single sensor, had no inherent cross check, and far more than the originally intended power over the rest of the flight systems.

If the photo I saw of "the sensor" was actually correct, and it worked like it looked,  it seemed basically an airflow affected vane sticking exposed out the side of the Fus, ready and waiting for impact with de-icer/step handler/cleaner/baggage handler/FOD/bird/drone (sorry, got carried away), it was an accident waiting to happen, and sadly it did, twice so far.

Money talks, but "saving money" talks louder.

We do not seem to learn that money and time spent on inspection and trouble shooting systems before they go live is essential.

In my business, far from aviation, they saved money by taking all the contract supervisors out, as they were stated as not needed as "the contractor will do the job to spec without supervision/audit".

Don't need to state how THAT went down! Did it kill anyone? Not that I know of, but a broken arm and an expensive closure due to a prohibition notice, Yes.

Cost evasion is evident at all levels!
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Offline lanicopter

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Re: It's a talking point. 737 Max series.
« Reply #13 on: April 15, 2019, 17:19:14 PM »
You do talk rubbish sometimes PDR and what's scary is people actually listen to you.

Your "10 mile stabilised approach" is absolutely false. Look up what "short final" means for instance. Or how about watch a few of the approaches into say, Toncontin International. Maybe after that look at the approach into Paro, both of which require instantaneous control inputs to avoid terrain right up to the runway threshold.

Approaches are to do with spacing of multiple aircraft, not because the aircraft need to be lined up perfectly for 10 miles or else they crash and burn.

Toncontin - notice this is a 757, appreciably larger than the 737-MAX
<a href="http://www.youtube.com/watch?v=O0ZcUS2nNd0" target="_blank">http://www.youtube.com/watch?v=O0ZcUS2nNd0</a>

Here's Paro in an Airbus A319
<a href="http://www.youtube.com/watch?v=N0KIlFqjams" target="_blank">http://www.youtube.com/watch?v=N0KIlFqjams</a>

And let's not forget Kai Tak with only a tiny 747-400
<a href="http://www.youtube.com/watch?v=YdVupou9ZZA" target="_blank">http://www.youtube.com/watch?v=YdVupou9ZZA</a>

Good luck with your ten seconds when 2 seconds could mean the difference between you being in the air or being in a tree :D

You do realise that the autopilot (when engaged) is making minute corrections to the aircraft based on real-time sensor data? It can only do so if the aircraft reacts to its inputs near instantaneously .... pilots don't have to think 10 seconds ahead at all, and nor do the autopilots.

You can absolutely make instant corrections to the attitude or course of an aircraft ....

Or in fact how about this pilot making an immediate correction when the plane was hit by Windshear at Madeira
<a href="http://www.youtube.com/watch?v=N2GNCoTG1zI" target="_blank">http://www.youtube.com/watch?v=N2GNCoTG1zI</a>

Sorry, but nonsense.


« Last Edit: April 15, 2019, 17:26:12 PM by lanicopter »
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Offline PDR

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Re: It's a talking point. 737 Max series.
« Reply #14 on: April 15, 2019, 19:39:28 PM »
I'm afraid you don't understand what it is you are seeing. But you will never accept that so there's little point in discussing it.

PDR
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Offline The Saint. (Owen)

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Re: It's a talking point. 737 Max series.
« Reply #15 on: April 15, 2019, 21:25:19 PM »
I know who I would rather believe first.  :study:
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Offline PDR

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Re: It's a talking point. 737 Max series.
« Reply #16 on: April 15, 2019, 22:24:09 PM »
True, but Cactus isn't here any more.

PDR
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Offline The Saint. (Owen)

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Re: It's a talking point. 737 Max series.
« Reply #17 on: April 15, 2019, 22:32:41 PM »
 ;D ;D ;D
Electrickery is the work of the devil.
Proper aeroplanes are powered by engines.

Offline lanicopter

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Re: It's a talking point. 737 Max series.
« Reply #18 on: April 15, 2019, 22:56:14 PM »
You're not going to believe me despite video evidence, lol - so arrogant.

Why do you think the pilot even has a yoke? Of course a plane can be manoeuvred.

The Toncontin RNAV approach into runway 02 (because i've used it as an example) can be automated until 2 DME from the runway, at which point the pilot is REQUIRED to manually and visually manoeuvre the aircraft to the runway threshold. They transition from both North + South via the TNT VOR, the approach consists of descending around a DME Arc (or more commonly nowadays via GPS waypoints which represent the same thing). Upon reaching the final waypoint they are approximately 2 miles South of the airport heading 090. At that point they are required as per the charts to command a visual, manual approach down to the runway. That would be a ~70 degree turn at 2 miles, manually controlled by the pilot. Or, a Go-Around is required.

Also explain to me VOR / DME Arc approaches into major airports? Offset ILS approaches? the Kai Tak IGS system? Non-precision approaches via NDBs? Full visual approaches?

What about the circling approach into LOWI (Innsbruck) between two mountainsides which is fully manual and regularly performed by 737s.

Yep - no idea what I'm talking about  ;D
« Last Edit: April 15, 2019, 22:57:30 PM by lanicopter »
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Offline PDR

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Re: It's a talking point. 737 Max series.
« Reply #19 on: April 16, 2019, 13:55:25 PM »
No, again clearly no idea what you're talking about. A stabilised approach doesn't have to be in a straight line - it's an approach profile with a closely defined path with designated speeds and altitudes at each stage of the path. The roll onto finals on the old Kai Tak approach had to be done well in advance, and while actually flying through the turn the yoke would be a long way over in the opposite direction arresting the roll-in and starting the roll out. But it's part of the stabilised approach path - any deviation beyond the (quite tight) speed, positoin and altitude limits means an abort.

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Re: It's a talking point. 737 Max series.
« Reply #20 on: April 16, 2019, 15:12:59 PM »
OK, I can go along with that. I have been in a 'blind' approach to EMA where the runway could not be seen for low cloud/fog until just before touchdown.  But talking about Kai Tak, an airline pilot friend (Virgin) told me he preferred that to the new airport, which suffers from abysmal side winds. How does the auto approach work when there is a bad crosswind- is that a case for a manual take over and a bootfull of rudder?

Offline PDR

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Re: It's a talking point. 737 Max series.
« Reply #21 on: April 16, 2019, 17:22:14 PM »
OK, I can go along with that. I have been in a 'blind' approach to EMA where the runway could not be seen for low cloud/fog until just before touchdown.  But talking about Kai Tak, an airline pilot friend (Virgin) told me he preferred that to the new airport, which suffers from abysmal side winds. How does the auto approach work when there is a bad crosswind- is that a case for a manual take over and a bootfull of rudder?

Airliners mostly ignore the drift error in crosswinds unless it is very large. They just fly down the approach pointing off the runway axis and let the tyres sort it out after impact touchdown. In a very large crosswind the pilot might be kicking in some rudder in the late approach, but flying a big, swept-wing beast with crossed controls isn't much fun so they do as little as they can get away with. Older aircraft like the 747 Classic only had 2-axis autopilots, so they had to be flown with manual rudder input in large crosswind components anyway. More modern machines have full three-axis AP plus autothrottles fed by inertial and barometric data so the flight control system can actually do the textbook crossed-control approach if it's cleared for it.

But if you look at a lot of the videos of airliners landing in crosswinds you can see that they usuall land "sideways" while travelling in the rinway direction, and then correct the heading after touchdown. 200tons of aeroplane will carry on straight down the runway regardless of which direction the tyres are pointing in for quite a long time - more than enough time for the pilot to re-point it!

PDR
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Offline lanicopter

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Re: It's a talking point. 737 Max series.
« Reply #22 on: April 16, 2019, 18:53:41 PM »
I do know what I'm talking about as it happens PDR.

It is you who said above that a plane had to be on a 10 mile stabilised approach because they couldn't be manoeuvred quickly enough by the pilot - which is utter nonsense.

I mean you only need to watch a airshow demo of an airliner to see how manoeuvrable they really are.

Again - the approach procedures at an airport are more to do with a) terrain avoidance, and b) aircraft / airway spacing than anything remotely related to the manoeuvrability of the aircraft.
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Offline PDR

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Re: It's a talking point. 737 Max series.
« Reply #23 on: April 16, 2019, 19:00:19 PM »
I mean you only need to watch a airshow demo of an airliner to see how manoeuvrable they really are.

At airshow weights (30 mins fuel, no pax, no freight) even my dog's kennel could be manoeuvrable.

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Re: It's a talking point. 737 Max series.
« Reply #24 on: April 17, 2019, 01:32:45 AM »
usuall land "sideways" while travelling in the rinway direction, and then correct the heading after touchdown. 200tons of aeroplane will carry on straight down the runway regardless of which direction the tyres are pointing in for quite a long time - more than enough time for the pilot to re-point it!

PDR

I can vouch for that...Returning to Manchester from Atlanta, December 2000, Boeing 777, I was in the left side looking out as we came in over Stockport. Imagine my surprise then as we descended and the world outside instead of going front...back, it was going away from the window at an angle and I realised we're having a cross wind landing...And that was fine, the undercarriage hit the tarmac and we straightened up.. THEN the port wing lifted and I thought "Oh dear, this might be messy" (Or something like that) at the same time as several of the clearly non Yorkshire folk onboard screamed, and screamed again when the wing came back down with a bang.
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Re: It's a talking point. 737 Max series.
« Reply #25 on: April 17, 2019, 01:46:52 AM »
I do know what I'm talking about as it happens PDR.

It is you who said above that a plane had to be on a 10 mile stabilised approach because they couldn't be manoeuvred quickly enough by the pilot - which is utter nonsense.

I mean you only need to watch a airshow demo of an airliner to see how manoeuvrable they really are.

Again - the approach procedures at an airport are more to do with a) terrain avoidance, and b) aircraft / airway spacing than anything remotely related to the manoeuvrability of the aircraft.

I'm sorry to be pedantic but Pete didn't say that:

Quote
Airliners are wallowy beasts and their controls only really "influence" rather than "direct" the aeroplane. Pilots have to be a long way ahead of the aeroplane to avoid problems. The3re are airliners which, once they have started pitching up, cannot avoid stalling even if the driver applies full forward stick 10 seconds before the stall happens. This isn't being "unstable" - it's just showing the effect of the inertia of a couple of hundred tons of aeroplane and fuel. That's why they have to be established on a 10-mile stabilised approach to have any hope of hitting the runway at anything close to the right speed (horizontal and vertical) while pointing in the right direction.

Can't a stabilised approach be human only? The landing videos above would say yes. Kai Tak isn't ILS after the checkerboard (I've only landed it on MS Flight Sim but I'm assuming the basics of navigation and approach are the same principle) but unless I made a great big crease in the runway (Often  :embarassed:) it was a stable approach.

Unless Newton had it all wrong the physics would say that there's a lot of inertia involved (A fully loaded A380 is 600 Tonnes) and will have been landed like that I would think to pass certification, but it will be stable doing it, but I sure wouldn't want to be thrown around the sky in it at that weight.
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Re: It's a talking point. 737 Max series.
« Reply #26 on: April 17, 2019, 08:12:59 AM »
Yes - a "stabilised approach" just means that the aeroplane has entered the approach in the right place, pointed in the right direction, at the right height and at the right speed, and then maintaining these four parameters within the defined limits (which change as the aeroplane proceeds) down the approach path. This can be done manually or in autopilot. Typical errors include "chasing the airspeed" in which the aeroplane starts the approach too fast and the pilot continually adds and removes power rather than having a constant power setting, and "lateral hunting" where the aeroplane hunts left & right because pilot fails to find the right heading to maintain the track on the runway centreline (or other defined approach path) in a crosswind.

It may also be worth mentioning (to further illustrate how assumptions based on light aircraft or model flying experience do't read across) that large aircraft like airliners aren't usually "flared" for touchdown - they have a target vertical velocity for the late-stage approach and they are just flown onto the runway at that VV and the undercarriage spring system soaks up the bump. There are several reasons for this. One is that several hundred tonnes of aeroplane has a lot of vertical inertia, and a few seconds of extra lift will only change that slightly. Another is that while it will only change it slightly it will make the touchdown point unpredictable, and that risks touching down too far down the runway (leaving insufficient runway to stop). But the main reason is that the need to get as much weight on the wheels as quickly as possible to minimise skidding and allow the brakes can work effectively. So an airliner is usually almost slammed into the runway, and glued there with spoilers, while the crew hit the brakes. There is no delicate holding-off and looking to delicately place the wheels on the ground at the moment of the stall as we were taught for the PPL!

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Re: It's a talking point. 737 Max series.
« Reply #27 on: April 17, 2019, 08:28:13 AM »
After a bad landing in Corfu, a Ryanair stewardess said " thank you for flying Ryanair, from Captain Kangaroo and the rest of us..."

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Re: It's a talking point. 737 Max series.
« Reply #28 on: April 17, 2019, 09:54:27 AM »
After a bad landing in Corfu, a Ryanair stewardess said " thank you for flying Ryanair, from Captain Kangaroo and the rest of us..."
;D ;D ;D ;D ;D
Mike
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Re: It's a talking point. 737 Max series.
« Reply #29 on: April 17, 2019, 10:00:36 AM »
Or the little old lady who, as she left the aeroplane, asked the Flight Attendant

"Young lady - did we land, or were we shot down?"

PDR
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Re: It's a talking point. 737 Max series.
« Reply #30 on: April 17, 2019, 10:54:13 AM »
 ;D
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Re: It's a talking point. 737 Max series.
« Reply #31 on: April 17, 2019, 12:23:24 PM »
At airshow weights (30 mins fuel, no pax, no freight) even my dog's kennel could be manoeuvrable.

PDR

And yet on the Toncontin approach which is fully manual, the aircraft still has remaining fuel, reserve fuel, cargo and passengers - is still fully under the pilots control. No automation is employed whatsoever except (in some cases) the autothrottle to maintain vRef (which you alluded to in a subsequent post).

Additionally, the aircraft absolutely has to be flared onto the runway on this approach because the approach angle is incredibly steep (and curved) due to terrain - not your standard glideslope which I believe is usually around 3 degrees.

So I'm sorry but you are incorrect - aircraft are absolutely capable of being manually controlled to a safe landing, and this is just one example of many. See also, Paro, Innsbruck.

In the case of the video into Toncontin that I posted - it is a 757-200. The difference between an empty and a fully loaded 752 is "only" 39,800kg .... it's MTOW is 116,000kg  - meaning its ZFW is 76,200kg ... hardly a dog kennel but as an aside, I highly doubt they only put 30 minutes of fuel into an airliner for an airshow performance anyway - so you're probably talking at a minimum of 85 tons of highly manoeuvrable metal.
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Re: It's a talking point. 737 Max series.
« Reply #32 on: April 17, 2019, 13:01:19 PM »
So I'm sorry but you are incorrect - aircraft are absolutely capable of being manually controlled to a safe landing,

And nowhere did I say they couldn't. You are reading things I haven't said, as others have pointed out already.

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Re: It's a talking point. 737 Max series.
« Reply #33 on: April 18, 2019, 17:23:19 PM »
Quote
Airliners are wallowy beasts and their controls only really "influence" rather than "direct" the aeroplane.
False, they directly control the aircraft. More quickly at higher speeds but that is why we have a vMC for minimum manoeuvrable control speed.

Quote from: PDR
Pilots have to be a long way ahead of the aeroplane to avoid problems.
They have to anticipate things, yes, but they can, as illustrated by the Madeira video, react immediately to situation requiring manual control - there was not 10 seconds to spare when windshear hit at ~40ft up and yet the aircraft was controlled successfully by the pilot.

Quote from: PDR
The3re are airliners which, once they have started pitching up, cannot avoid stalling even if the driver applies full forward stick 10 seconds before the stall happens. This isn't being "unstable" - it's just showing the effect of the inertia of a couple of hundred tons of aeroplane and fuel.

The fuel weight has very little to do with the pitching up/down capabilities of the aircraft as the tanks are positioned around the CoG and compensated for via pitch trim.

The aircraft will handle pretty much the same in terms of pitch whether it be fully loaded, or on a final approach.

I would appreciate an example of an airliner being flown in the confines of a normal flight envelope where it would be unable to recover from a stall if it was flying at or above vRef within 10 seconds of the yoke being pushed forward. I'm genuinely interested.

Quote from: PDR
That's why they have to be established on a 10-mile stabilised approach to have any hope of hitting the runway at anything close to the right speed (horizontal and vertical) while pointing in the right direction.

They don't - see the above examples, the stabilised approach is more to do with spacing of aircraft than single aircraft maneoverability. Those 747s you see flying into Kai Tak were on an expected flight profile (thanks to the approach plate) but not "stable" in terms of landing because they still needed to be directed onto the runway by the pilot.  Even IGS (not ILS) would be making subtle control inputs to make sure that the aircraft stayed on profile during the approach and it would need to be able to do that based on conditions in the air at the time - for example, gusting crosswinds.

Quote from: PDR
Picture trying to park a fully-loaded bus in a parking bay on an ice-rink while having a minimum speed of 160mph for all but the last 30 yards - it's a bit like that only harder.

Except it's nothing like that. It's like directing a 100 ton aircraft onto a runway with flight control surfaces that were designed for that very purpose.
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Re: It's a talking point. 737 Max series.
« Reply #34 on: April 18, 2019, 21:24:16 PM »
The fuel weight has very little to do with the pitching up/down capabilities of the aircraft as the tanks are positioned around the CoG

The fuel is largely stored in wing tanks (actually sealed up sections of the wing structure). The wings of a typical airliner are swept, so the fuel in the inboard portions of the tanks is in front of the CG while the fuel in the outboard sections of the tanks is behind the CG. The centre of mass of the fuel may be close to the CG, but it is longitudinally distributed, so it has a significant moment of inertia. To pitch the aeroplane up or down the control force from the elevator/tailplane must first overcome the longitudinal inertia to start the rotation, and then you have to overcome the resulting angular momentum to stop the rotation again. The moment of inertia imparted by 20-odd tonnes of fuel significantly impinges on the handling.

Quote
...and compensated for via pitch trim.

You cannot compensate for angular inertia with trim. Google is not a substitute for actually understanding stuff.

Look you can believe what you like - I don't actually care. Questions were asked and I contributed some answers. Whether people like the answers or don't is entirely up to them.

PDR
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Re: It's a talking point. 737 Max series.
« Reply #35 on: April 18, 2019, 22:17:08 PM »
Why do they measure the fuel by weight rather than litres/gallons?
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Re: It's a talking point. 737 Max series.
« Reply #36 on: April 19, 2019, 01:07:36 AM »
Why do they measure the fuel by weight rather than litres/gallons?


I'm guessing here but I would think that weight is paramount to the pilot and as long as it says 'Full' on the dash he doesn't need to know what the volume is but does need to know how much weight he's dragging into the sky (Take off speeds/runway length etc).
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Re: It's a talking point. 737 Max series.
« Reply #37 on: April 19, 2019, 07:13:22 AM »

I'm guessing here but I would think that weight is paramount to the pilot and as long as it says 'Full' on the dash he doesn't need to know what the volume is but does need to know how much weight he's dragging into the sky (Take off speeds/runway length etc).

That's one reason. Another is that the weight remains constant but the volume changes with temperature. The amount of impulse (thrust x time) you get from a given quantity of fuel relates to the mass of the fuel rather than the space it occupies, so if a pilot knows there is 10,000lbs of fuel on board the he knows that will give cruise power for 2 hours. If it was measured in gallans he'd need tio correct it for temperature to find out. Remember that if an airliner takes on fuel in (say) Texas for a long-haul flight then the fuel could be at 35degC when it's put in the tanks, but after an hour at 35,000ft it could be at -50degC, over which range the volume would drop by around 10%. Aircraft used to measure fuel in lbs, but as the world migrates from inferial to metric measures an increasing number use kg. There have been errors where this transition occured on the same aeroplane (cf The Gimli Glider).

Having said that there ARE aeroplanes which use fuel measured in gallons or litres. There used to be a general convention that AvGas (petrol, for piston engines) was measured in gallons while AvTur (kerosene, for turbines) was measured in lbs, but I think that only remains for small aeroplanes where the fuel weights might be less significant. I don't think any airliners use volume measures, but I could be wrong on that.

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Re: It's a talking point. 737 Max series.
« Reply #38 on: April 19, 2019, 08:12:33 AM »
That's one reason. Another is that the weight remains constant but the volume changes with temperature. The amount of impulse (thrust x time) you get from a given quantity of fuel relates to the mass of the fuel rather than the space it occupies, so if a pilot knows there is 10,000lbs of fuel on board the he knows that will give cruise power for 2 hours. If it was measured in gallans he'd need tio correct it for temperature to find out. Remember that if an airliner takes on fuel in (say) Texas for a long-haul flight then the fuel could be at 35degC when it's put in the tanks, but after an hour at 35,000ft it could be at -50degC, over which range the volume would drop by around 10%. Aircraft used to measure fuel in lbs, but as the world migrates from inferial to metric measures an increasing number use kg. There have been errors where this transition occured on the same aeroplane (cf The Gimli Glider).

Having said that there ARE aeroplanes which use fuel measured in gallons or litres. There used to be a general convention that AvGas (petrol, for piston engines) was measured in gallons while AvTur (kerosene, for turbines) was measured in lbs, but I think that only remains for small aeroplanes where the fuel weights might be less significant. I don't think any airliners use volume measures, but I could be wrong on that.

PDR
I think it is normal to talk of tons with airliner fuel. I remember an airline captain friend commenting once that he liked an extra ton of fuel on board when coming in to Orlando, as it helped damp out the turbulence there. (inertia again?)

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Re: It's a talking point. 737 Max series.
« Reply #39 on: April 19, 2019, 11:18:00 AM »
Thank you Peter, your explanation makes perfect sense.  :af :af
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