FlyHappy
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Air Transat Flight 236: questions for pilots and other experts

Sat Jun 02, 2018 6:09 pm

I just became aware of the details of this event, and I have questions if any A330/Airbus rated pilots in particular, would care to chime in on.

Its clear that a failure in the maintenance and supervisory process led to the incorrect component installation, leading to the chafing of the fuel line and eventual rupture.

Its also clear that the pilots did a masterful job during the final, powerless glide phase to put the aircraft down safely, on an island airfield in the middle of the night. Those pilots demonstrated a high proficiency to perform with no margin for error.

But the fuel management is the central question, and something I cannot really comprehend as a lay person.

I've read that the SOP of Air Transat itself, specifically directed the pilots to cross-feed the fuel tanks due to an imbalance alert. Is this true, in an absolute sense? Did the pilots perform the correct action, strictly based on the carriers procedure?

I understand that some experts/pilots feel the this crew failed to diagnose fuel loss in a reasonable amount of time and/or neglected to stop the cross-feed process when they could have to prevent flame-out of the remaining engine. This area is very, very unclear to me; for example, I don't know when the cross-feed was halted (perhaps not at all?). Does anyone know at what point in the flight, there would have been enough fuel remaining to make a single engine landing?

Based on information available to the pilots and procedures in that era, do you believe that the pilots errored in a way that most pilots would not? Was there a widely understood/practiced procedure that they did not perform and reasonably could have, given time and workload?

It seems afterwards, there was an AD issued related to use of cross-feed and modification to Airbus computer logic to increase awareness of fuel use. Do these things somewhat vindicate the pilots, that expecting them to triage this indirectly isn't always realistic? What is the consequence to flight characteristics of flying "imbalanced" when fuel leak does empty one side?

Unrelated: running under RAT power, what controls are available to the pilots? what controls allow the pilot perform the S turns necessary to drop altitude, and whats the stall speed of the aircraft, given the lack of flaps/spoilers?

I've searched and see some very old threads on the is topic, but I'm curious in general how you Pilots today, view the actions and performance of the 236 crew.
 
ExMilitaryEng
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Re: Air Transat Flight 236: questions for pilots and other experts

Tue Jun 05, 2018 1:32 am

FWIW, not too long after, when they ran this exact same faults scenario on simulators; all pilots crashed. (Most failed to properly assess the fuel leak, and none got to glide the plane to safety)
 
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Starlionblue
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Re: Air Transat Flight 236: questions for pilots and other experts

Tue Jun 05, 2018 2:18 am

To answer the systems question of what happens with RAT generation only.

With both engines flamed out, you'd have the RAT, meaning the Green hydraulic system only. Hydraulic flow is between 15% and 45% of normal so the controls you have would be sluggish.

Control would be in Alternate Law, meaning some protections are gone.
- Pitch control. Authority reduced. Both elevators but no trimmable stabiliser.
- Yaw control. Rudder is available.
- Roll control. Only 2 spoilers per wing, but you'd still have all four ailerons.
- Flaps and slats are available but slow. The QRH summary says "Use Flap 2".
- Landing gear would need to be gravity extended.

Electrics would be generated by the Emergency Generator, running off Green hydraulic system pressure. Normally you'd have 2 engine driven generators giving 115KVA each. On the RAT you get a whopping 8KVA until you go under 260 knots, at which point you get only 3.5KVA. In a masterful understatement, the FCOM says "leading to some shedding". :D
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
kalvado
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Re: Air Transat Flight 236: questions for pilots and other experts

Tue Jun 05, 2018 11:57 am

Starlionblue wrote:
Electrics would be generated by the Emergency Generator, running off Green hydraulic system pressure. Normally you'd have 2 engine driven generators giving 115KVA each. On the RAT you get a whopping 8KVA until you go under 260 knots, at which point you get only 3.5KVA. In a masterful understatement, the FCOM says "leading to some shedding". :D

What about batteries? Looks like A330 has about 2 kWt-h worth of batteries. When does that come into play?
 
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zeke
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Re: Air Transat Flight 236: questions for pilots and other experts

Tue Jun 05, 2018 1:14 pm

FlyHappy wrote:
Does anyone know at what point in the flight, there would have been enough fuel remaining to make a single engine landing?

Based on information available to the pilots and procedures in that era, do you believe that the pilots errored in a way that most pilots would not? Was there a widely understood/practiced procedure that they did not perform and reasonably could have, given time and workload?

Unrelated: running under RAT power, what controls are available to the pilots? what controls allow the pilot perform the S turns necessary to drop altitude, and whats the stall speed of the aircraft, given the lack of flaps/spoilers?[twoid][/twoid]


I’ll try and answer those 3 points.

Firstly before they turned the cross feed on they had more than enough fuel to make a single engine landing.

Secondly with the benefit of hindsight in a zero g zero airspeed environment I would honestly say I probably would have done things differently. In all my years flying FBW Airbus aircraft I have never had to turn the crossfeed on in flight to balance the tanks. The main reason for that is the forward transfer from trim tank automatically evens the tank levels out. Having the tanks uneven in my mind would have triggered curiosity as to why ?

Thirdly with the engines flamed out the aircraft with enough forward speed basically will be running on 3 rats, the engines are still spinning by the air being forced through them which would drive the hydraulic pumps, the actual rat would be deployed because the generators are offline providing additional hydraulic pressure which will power the emergency generator.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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Starlionblue
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Re: Air Transat Flight 236: questions for pilots and other experts

Tue Jun 05, 2018 1:23 pm

kalvado wrote:
Starlionblue wrote:
Electrics would be generated by the Emergency Generator, running off Green hydraulic system pressure. Normally you'd have 2 engine driven generators giving 115KVA each. On the RAT you get a whopping 8KVA until you go under 260 knots, at which point you get only 3.5KVA. In a masterful understatement, the FCOM says "leading to some shedding". :D

What about batteries? Looks like A330 has about 2 kWt-h worth of batteries. When does that come into play?


We do indeed have batteries. 2 main ones and one for APU start. The batteries are used before start and after shutdown (if you don't have external power). They are also used in emergencies but AFAIK, they don't have nearly enough capacity to run hydraulics, and without hydraulics you're toast. Which is why the RAT powers the green hydraulic system directly, and the green hydraulic system runs the emergency generator.

Personal note: The 330 electrics were obviously designed with the primary goal of driving new pilots to the type crazy, and giving checkers lots of things to ask you about. And don't get me started on the fuel system. :D
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
FlyHappy
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Re: Air Transat Flight 236: questions for pilots and other experts

Wed Jun 06, 2018 12:16 am

thanks to all for contributions thus far, I really appreciate it.

zeke wrote:

Firstly before they turned the cross feed on they had more than enough fuel to make a single engine landing.


I should have been more precise in my question - is it clear in terms of chronology, at what point in the events (starting at fuel imbalance indication to 2nd engine fuel starvation) the cross feed valve could have been closed, preserving enough fuel to make a powered landing? I don't even know if the valve was ever closed; basically I'm asking how much time this crew had to figure out that a fuel was responsible (until they did or didn't....)

zeke wrote:
Secondly with the benefit of hindsight in a zero g zero airspeed environment I would honestly say I probably would have done things differently. In all my years flying FBW Airbus aircraft I have never had to turn the crossfeed on in flight to balance the tanks. The main reason for that is the forward transfer from trim tank automatically evens the tank levels out. Having the tanks uneven in my mind would have triggered curiosity as to why ?


I dont know what "zero g zero" means ;) But I get that you are saying that you feel you would have more thoroughly questioned the reason for the imbalance. Did the crew in fact, open the valve, "by the book", per a standard procedure ? What is the purpose/"correct use case" of the cross feed valve - is it just to supply the other side with fuel in the case of an engine shutdown (thus no consumption)? Is there any other reason to do so? Is safe flying possible with severely imbalanced wing tanks?


ExMilitaryEng wrote:
FWIW, not too long after, when they ran this exact same faults scenario on simulators; all pilots crashed. (Most failed to properly assess the fuel leak, and none got to glide the plane to safety)


Are you saying these simulations were done as part of the investigation? If many peer pilots did not also assess the leak, is it reasonable that the investigating body still assigned partial responsibility to the pilots?
 
BoeingGuy
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Re: Air Transat Flight 236: questions for pilots and other experts

Wed Jun 06, 2018 12:55 am

Starlionblue wrote:
kalvado wrote:
Starlionblue wrote:
Electrics would be generated by the Emergency Generator, running off Green hydraulic system pressure. Normally you'd have 2 engine driven generators giving 115KVA each. On the RAT you get a whopping 8KVA until you go under 260 knots, at which point you get only 3.5KVA. In a masterful understatement, the FCOM says "leading to some shedding". :D

What about batteries? Looks like A330 has about 2 kWt-h worth of batteries. When does that come into play?


We do indeed have batteries. 2 main ones and one for APU start. The batteries are used before start and after shutdown (if you don't have external power). They are also used in emergencies but AFAIK, they don't have nearly enough capacity to run hydraulics, and without hydraulics you're toast. Which is why the RAT powers the green hydraulic system directly, and the green hydraulic system runs the emergency generator.

Personal note: The 330 electrics were obviously designed with the primary goal of driving new pilots to the type crazy, and giving checkers lots of things to ask you about. And don't get me started on the fuel system. :D


On Boeing airplanes, only a limited number of systems are powered by the battery. I’m assuming the A330 is similar in this regard. The electric driven primary and demand Hydraulic pumps are not driven from battery. If the APU is running, that would power the electrical driven pumps. Obviously in this case they had no APU.

Does the A330 RAT generate electric power also? It does on the 777 and 787, but from previous comments I’m inferring the A330 RAT does not.

I bet Zeke’s comment about “zero g zero airspeed” refers to that fact that he’s sitting on the ground, not in flight in a stressful emergency. I’ve heard it called “Zero Knot”.

It’s easy for me to sit at my desk relaxed and well rested with a cup of coffee and say, “that procedure is easy to understand” or “they should have figured that out” or “any Pilot should have known that.”

However, it may not be clear to a pilot who’s stressed in an emergency, fatigued, jet lagged, and has 200 lives sitting behind him. Maybe English isn’t your first language, etc.

People who design flight procedures and flight deck interfaces keep this in mind (or should).
 
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Starlionblue
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Re: Air Transat Flight 236: questions for pilots and other experts

Wed Jun 06, 2018 1:38 am

BoeingGuy wrote:
Starlionblue wrote:
kalvado wrote:
What about batteries? Looks like A330 has about 2 kWt-h worth of batteries. When does that come into play?


We do indeed have batteries. 2 main ones and one for APU start. The batteries are used before start and after shutdown (if you don't have external power). They are also used in emergencies but AFAIK, they don't have nearly enough capacity to run hydraulics, and without hydraulics you're toast. Which is why the RAT powers the green hydraulic system directly, and the green hydraulic system runs the emergency generator.

Personal note: The 330 electrics were obviously designed with the primary goal of driving new pilots to the type crazy, and giving checkers lots of things to ask you about. And don't get me started on the fuel system. :D


On Boeing airplanes, only a limited number of systems are powered by the battery. I’m assuming the A330 is similar in this regard. The electric driven primary and demand Hydraulic pumps are not driven from battery. If the APU is running, that would power the electrical driven pumps. Obviously in this case they had no APU.

Does the A330 RAT generate electric power also? It does on the 777 and 787, but from previous comments I’m inferring the A330 RAT does not.
.


As you say it's similar on Airbus. The batteries will power some buses only, specifically AC and DC essential and land recovery buses (AC is generated from DC through the static inverter).

Indeed the 330 RAT does not generate electric power. It powers the green hydraulic system only. In turn, the green hydraulic system can power the emergency electric generator.

So, if you lost both engines and didn't have the APU, you would be on batteries, with very limited electrics, and with the RAT providing limited hydraulics. The emergency generator would start, giving you back some additional AC and DC buses. AC would now be generated directly by the emergency generator. The transition to emer elec is somewhat disconcerting, as basically everything in the cockpit goes dark for a few seconds, then the captain's side instruments come back on.

If you did at this point manage to restart an engine or start the APU, and thus the associated generator, you'd get most everything back except some galley and commercial loads. However, you'd still be in emergency electrical configuration since the emergency generator keeps running to supply "its" buses.


The 350 is a different kettle of fish. The RAT drives the emergency generator directly, and the generator provides (some) AC electrical power. You don't need backup hydraulic generation at all since the Electro-Hydrostatic and Electrical Backup Hydraulic Actuators (EHAs and EBHAs) work independently of the hydraulic systems. The EHAs have their own electric hydraulic pumps and a self-contained hydraulic reservoir and are thus completely independent of the hydraulic systems. The EBHAs act like conventional actuators when their "main" hydraulic system is available, and like an EHA if hydraulic pressure is lost.
Last edited by Starlionblue on Wed Jun 06, 2018 1:58 am, edited 1 time in total.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
BoeingGuy
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Re: Air Transat Flight 236: questions for pilots and other experts

Wed Jun 06, 2018 1:49 am

Starlionblue wrote:
BoeingGuy wrote:
Starlionblue wrote:

We do indeed have batteries. 2 main ones and one for APU start. The batteries are used before start and after shutdown (if you don't have external power). They are also used in emergencies but AFAIK, they don't have nearly enough capacity to run hydraulics, and without hydraulics you're toast. Which is why the RAT powers the green hydraulic system directly, and the green hydraulic system runs the emergency generator.

Personal note: The 330 electrics were obviously designed with the primary goal of driving new pilots to the type crazy, and giving checkers lots of things to ask you about. And don't get me started on the fuel system. :D


On Boeing airplanes, only a limited number of systems are powered by the battery. I’m assuming the A330 is similar in this regard. The electric driven primary and demand Hydraulic pumps are not driven from battery. If the APU is running, that would power the electrical driven pumps. Obviously in this case they had no APU.

Does the A330 RAT generate electric power also? It does on the 777 and 787, but from previous comments I’m inferring the A330 RAT does not.
.


As you say it's similar on Airbus. The batteries will power some buses only, specifically AC and DC essential and land recovery buses (AC is generated from DC through the static inverter).

Indeed the 330 RAT does not generate electric power. It powers the green hydraulic system only. In turn, the green hydraulic system can power the emergency electric generator.

So, if you lost both engines and didn't have the APU, you would be on batteries, with very limited electrics, and with the RAT providing limited hydraulics. The emergency generator would start, giving you back some additional AC and DC buses. AC would now be generated directly by the emergency generator. The transition to emer elec is somewhat disconcerting, as basically everything in the cockpit goes dark for a few seconds, then the captain's side instruments come back on.

If you did at this point manage to restart an engine or start the APU, and thus the associated generator, you'd get most everything back except some galley and commercial loads. However, you'd still be in emergency electrical configuration since the emergency generator keeps running to supply "its" buses.


The 350 is a different kettle of fish. The RAT drives the emergency generator directly, and the generator provides (some) AC electrical power. You don't need emergency hydraulic generation at all since the Electro-Hydrostatic and Electrical Backup Hydraulic Actuators (EHAs and EBHAs) work independently of the hydraulic systems. The EHAs have their own electric hydraulic pumps and a self-contained hydraulic reservoir and are thus completely independent of the hydraulic systems. The EBHAs act like conventional actuators when their "main" hydraulic system is available, and like an EHA if hydraulic pressure is lost.


The A330 is like the 757/767 then. ETOPS 757s and 767s have a Hydraulic Motor Generator (HMG) powered by the Center Hydraulic System, which in turn is powered from the RAT like how you describe. The HMG will power some more systems than the battery only, but still limited.

The 777 RAT powers both Electric and Hydraulics. The 787 RAT only provides Electric power, which in term would power some electric driven Hydraulic pumps.
 
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Starlionblue
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Re: Air Transat Flight 236: questions for pilots and other experts

Wed Jun 06, 2018 1:58 am

Sounds about right. I suppose the significant difference between the 787 and the 350 in this regard is the EHAs and EBHAs removing the need for backup hydraulic generation, so the RAT doesn't power hydraulics even indirectly.
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