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LeCoqFrancais
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What we’ve learned from Eastern Air Lines flight 902

Sat Aug 27, 2016 2:02 pm

Student pilots are taught very early on to recognize that when an airplane approaches its minimum flying speed, the airflow over the wing will begin to separate or break down, creating turbulence over the tail. The degradation of lift and the associated turbulence over the tail causes the airplane to buffet and alert the pilot to a deteriorating and dangerous situation. The recovery is rather basic – lower the nose some, apply full power to the engine and let the airplane fly out of it. As it accelerates, the buffeting will end and the aircraft will safely regain both flight and controllability.
In the 1930’s, military and large civilian airplanes were being equipped with supercharged and turbocharged engines. These engines enabled the planes to fly higher and faster than airplanes with normal engines. However, these “boosted” engines required a pilot with a delicate hand on the throttles. Whereas a normally aspirated engine could run at full throttle continuously without much more than some added wear, the supercharged and turbocharged engines would run beyond the normal power limits creating excessive heat which, in minutes, would damage the engine. Only when the situation was critical could a competent pilot consider “firewalling” the throttles by pushing them to the stops and exceeding the manufacturers’ limits.

http://www.nycaviation.com/2014/10/disa ... 8GSYbWi3bF
--
What is everybodies opinion on this?
Sébastien C. Tourillon
 
WIederling
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Joined: Sun Sep 13, 2015 2:15 pm

Re: What we’ve learned from Eastern Air Lines flight 902

Sun Aug 28, 2016 8:09 am

Stall: not all types exibit benign stall behaviour. That is the reason why "artificial stall behaviour" aka "stick shaker" was introduced.

diesels and turbocharged machines are suicide designs.
i.e. uncontrolled the engine will over rev and destruct.

In diesel engines this is fixed via a governor. ( thus with a basic diesel engine the throttle controls rpm in first order and not power)
in turbocharged engines you need to limit boost pressure otherwise the increase in energetic exhaust will increase boost pressure for even more and hotter exhaust in an accelerating spiral until things separate :-)
Murphy is an optimist
 
rcair1
Posts: 1147
Joined: Wed Oct 28, 2009 8:39 pm

Re: What we’ve learned from Eastern Air Lines flight 902

Wed Aug 31, 2016 2:30 pm

LeCoqFrancais wrote:
Student pilots are taught very early on to recognize that when an airplane approaches its minimum flying speed, the airflow over the wing will begin to separate or break down, creating turbulence over the tail. The degradation of lift and the associated turbulence over the tail causes the airplane to buffet and alert the pilot to a deteriorating and dangerous situation. The recovery is rather basic – lower the nose some, apply full power to the engine and let the airplane fly out of it. As it accelerates, the buffeting will end and the aircraft will safely regain both flight and controllability.
In the 1930’s, military and large civilian airplanes were being equipped with supercharged and turbocharged engines. These engines enabled the planes to fly higher and faster than airplanes with normal engines. However, these “boosted” engines required a pilot with a delicate hand on the throttles. Whereas a normally aspirated engine could run at full throttle continuously without much more than some added wear, the supercharged and turbocharged engines would run beyond the normal power limits creating excessive heat which, in minutes, would damage the engine. Only when the situation was critical could a competent pilot consider “firewalling” the throttles by pushing them to the stops and exceeding the manufacturers’ limits.

http://www.nycaviation.com/2014/10/disa ... 8GSYbWi3bF
--
What is everybodies opinion on this?

While I'm not an ATP and have never flown big jets (any jets), my understanding is that stall recovery in a large airline transport aircraft is not as simple as the small GA aircraft most students stall and spin (like I did). This is even more important at high altitude - where a recovery is much more difficult and different.
A few reasons
- Under-slung engines create a upward nose moment when 'firewalled' - you push the throttle forward and the aircraft will pitch up. I believe that at altitude that moment can be greater than elevator authority to pitch down, or will require nose down trim in addition to nose down elevator.
- A swept wing stalls in a very different fashion with the most rear part stalling first. That also creates a nose up moment.
- At high altitude the margins between overspeed and stall are very small - and engines don't have as much power - meaning recovery at high altitude is harder.

Check out this video from Aviation Week on a simulated full stall in a 737. Notice how the, as the pilot pitches up out of the dive he re-stalls the wing several times. Pitch control is critical. (Start about 3:30 in the video).
https://youtu.be/zCJco59tqoQ

Note - the issue here is why the FAA is mandating more training on recovery from unusual attitudes and why airlines are starting to do it. The video above is a simulator certified for this type of training.

WIederling wrote:
Stall: not all types exibit benign stall behaviour. That is the reason why "artificial stall behaviour" aka "stick shaker" was introduced.

diesels and turbocharged machines are suicide designs.
i.e. uncontrolled the engine will over rev and destruct.

In diesel engines this is fixed via a governor. ( thus with a basic diesel engine the throttle controls rpm in first order and not power)
in turbocharged engines you need to limit boost pressure otherwise the increase in energetic exhaust will increase boost pressure for even more and hotter exhaust in an accelerating spiral until things separate :-)[/quote]

That is correct, the approach from the airlines and pilots have been "Avoid the stall." There has been little emphasis or training on recovery because "you never get there". As we all know, that is not the case, and changes in training requirements reflect that.

WIederling wrote:
diesels and turbocharged machines are suicide designs.
i.e. uncontrolled the engine will over rev and destruct.

In diesel engines this is fixed via a governor. ( thus with a basic diesel engine the throttle controls rpm in first order and not power)
in turbocharged engines you need to limit boost pressure otherwise the increase in energetic exhaust will increase boost pressure for even more and hotter exhaust in an accelerating spiral until things separate :-)

This cracked me up. Never thought of them as "suicide designs", but you have a good point.
I used to have a tractor with a Detroit Diesel 3-73 engine (3 cylinders, each 73 cubic inches). The engine was a supercharged 2-cycle diesel design and it had an 'emergency cutoff' in case it over-ran. That cutoff was a spring loaded plate that slammed against the air intake when you pulled a release cable. Instantly shut down the engine.
That engine was a riot. Because it was a 2-cycle it fired every rotation and sounded like it was screaming along at twice the speed of normal 4-cycle engines. It just howled along.

This type of Detroit Diesel was quite common for many years - but rare now. They were specified in terms of number of cylinders and size of each cylinder and also the configuration, inline, flat, V
Here is a video of a Detroit Diesel 6V92 powered truck. 6 cyliners, V-configuration, 92 cubic inches per cylinder. That's a big engine and because it is 2 cycle, produces lots of power.
https://youtu.be/m4Vw9v0khIY
rcair1
 
hivue
Posts: 2115
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Re: What we’ve learned from Eastern Air Lines flight 902

Wed Aug 31, 2016 9:09 pm

The article implies "firewalling" the throttles as SOP when severe wind shear is encountered, and that firewalling damages engines. Is "firewalling" the same as TOGA power? If it is not, is TOGA used in severe wind shear situations? I assume TOGA does not present much of a threat of engine damage, but that would suggest that a flight crew using TOGA might not have all the thrust that is possible available to them in a really bad situation.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
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longhauler
Posts: 6488
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Re: What we’ve learned from Eastern Air Lines flight 902

Wed Aug 31, 2016 10:40 pm

hivue wrote:
The article implies "firewalling" the throttles as SOP when severe wind shear is encountered, and that firewalling damages engines. Is "firewalling" the same as TOGA power? If it is not, is TOGA used in severe wind shear situations? I assume TOGA does not present much of a threat of engine damage, but that would suggest that a flight crew using TOGA might not have all the thrust that is possible available to them in a really bad situation.

With engines equipped with FADEC, TOGA or Maximum Thrust is the same as "firewalling" the engines. You push the thrust levers right to the stops and you will get the maximum power the engines can safely produce as certified. It is not the most the engines can produce, but it IS the most the pilots can get. I am assuming certification requirements for the airframe dictate that it is enough.

However ...

I remember many years ago when I flew the B737-200, our rudimentary windshear (and/or ground contact) recovery techniques for the day dictated that we "firewall" the engines. These were JT8D-9As, no FADEC, nothing fancy, just plain old EPR gauges with bugs set using charts. I remember one day doing an approach into YYZ, the EPR bugs were set to 1.98 EPR for a go-around per SOP.

We encountered a suspected windshear and started a go-around using 1.98 EPR. When it was clear this WAS a windshear we firewalled the engines and got about 2.10 EPR and we just about went straight up!!! (Gotta love P&W engines). Had the aircraft been FADEC equipped, 1.98 would have been all we would get. Would that have been enough? ... I'll never know ... but 2.10 was sure as hell enough!
Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!
 
OzzyPirate
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Re: What we’ve learned from Eastern Air Lines flight 902

Wed Aug 31, 2016 11:00 pm

hivue wrote:
The article implies "firewalling" the throttles as SOP when severe wind shear is encountered, and that firewalling damages engines. Is "firewalling" the same as TOGA power? If it is not, is TOGA used in severe wind shear situations? I assume TOGA does not present much of a threat of engine damage, but that would suggest that a flight crew using TOGA might not have all the thrust that is possible available to them in a really bad situation.


Not in modern FADEC jet engines, no. To use the 737NG as an example (as that's what I know), "TOGA" is not a specific thrust setting. It is simply a mode of operation in which the commanded thrust will be at a predetermined N1. A reduced thrust takeoff using a high assumed temperature will still involve "TOGA" operation, but the engines may be as low as 86-87% N1. Similar for a single push of the TOGA switches during an all-engine go-around.

To answer the second part of your question, firewalling the thrust levers (pushing them to the forward stop) is a legitimate action in many cases. On the 737, this will achieve maximum rated thrust from the engine (which will in almost all cases be above the calculated TOGA limit), while N1/N2 overspeed protection is maintained. Assuming the EECs (the engine's electronic brain) are not in a degraded mode, the only threat of exceedance is from EGT, which is not protected. The 737 windshear escape and GPWS warning (terrain escape) maneuvers require "aggressively applying maximum thrust", which essentially means firewalling the levers without delay.

I understand Airbus terminology is slightly different, in that "TOGA" is not used for a reduced thrust takeoff, but someone else can clarify that.
 
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Starlionblue
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Re: What we’ve learned from Eastern Air Lines flight 902

Wed Aug 31, 2016 11:45 pm

rcair1 wrote:
While I'm not an ATP and have never flown big jets (any jets), my understanding is that stall recovery in a large airline transport aircraft is not as simple as the small GA aircraft most students stall and spin (like I did). This is even more important at high altitude - where a recovery is much more difficult and different.
A few reasons
- Under-slung engines create a upward nose moment when 'firewalled' - you push the throttle forward and the aircraft will pitch up. I believe that at altitude that moment can be greater than elevator authority to pitch down, or will require nose down trim in addition to nose down elevator.
- A swept wing stalls in a very different fashion with the most rear part stalling first. That also creates a nose up moment.
- At high altitude the margins between overspeed and stall are very small - and engines don't have as much power - meaning recovery at high altitude is harder.

Check out this video from Aviation Week on a simulated full stall in a 737. Notice how the, as the pilot pitches up out of the dive he re-stalls the wing several times. Pitch control is critical. (Start about 3:30 in the video).
https://youtu.be/zCJco59tqoQ

Note - the issue here is why the FAA is mandating more training on recovery from unusual attitudes and why airlines are starting to do it. The video above is a simulator certified for this type of training.


Stall recovery in an airliner is indeed different. At high altitude, immediately pushing the thrust levers all the way forward will make things harder. Granted, we are almost at max thrust in the cruise anyway so it's not like we get much more, but in any case getting the nose down and unstalling the wing should be done before (gently) pushing the thrust levers forward. At all times you have to be very very gently in pitch control, especially when recovering the nose back up. It is super-easy to get into a secondary stall.

Given an unchanged angle of incidence along the span, swept wings should have a tendency to stall tip first. However most are washed out, meaning they have a higher angle of incidence near the root. This gives them much more bening stall characteristics, with a more natural pitch down tendency. It is a certification requirement for an airliner to have benign stall tendencies or mechanisms to help out in case they aren't that benign, which is why you have stick pushers or in the case of Airbus, alpha protection.

Certainly a lot of training has been introduced or changed in the past few years. Maintaining altitude during high altitude upsets is frowned upon. You have plenty of room down to the ground. Get the nose down and the speed up. On the other hand if you're stalling at low altitude, say under 10000ft, you don't push the nose down nearly as much. The air is thicker so you'll recover faster, and besides the ground is closer.

To add a wrinkle, on the Airbus we are taught to act differently if we doing a "low speed recovery" (in normal law) compared to a stall recovery (in a degraded law). In the first case, all the protections are available, so going to TOGA immediately is good and proper. In the second case the wing is already stalled, so must be unstalled first, and to add to that we don't have alpha protection. (Don't know how the Boeing guys do it.)


OzzyPirate wrote:

I understand Airbus terminology is slightly different, in that "TOGA" is not used for a reduced thrust takeoff, but someone else can clarify that.


The TOGA detent is used for TOGA (max thrust) take-off and for derated take-off. However most of our take-offs use the MCT/FLEX detent. FLEX is assumed temperature thrust.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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