American investigates as 777 engine fails to respond to throttle

[Huck]

It's considered bad form to have spoilers out with anything above idle thrust, at least in the Mighty Dog 11. With spoilers deployed I keep my forearm against the PLA's, just so I know if the autothrottles are coming up. Yes, from the right seat.

[Orestes]

Engine inlet conditions?

So far, most of the speculation on the cause of the BA038 crash has focused on computer control (EMI? Software?) or fuel issues (Low fuel?Cold fuel? Water/ice? Waxing?).
This new info regarding the American Airlines 777 engine that failed to throttle up (and the little anecdote above regarding a mysterious Continental engine shutdown on approach) has led me to wonder if we've been ignoring a possible aerodynamic cause - i.e. engine inlet conditions? These incidents seem to have all occurred at the same point in the flight envelope - low & slow, high AOA on approach.

Any opinions?

[Oluf Husted]

"Captain Nut"

Dear Orestes,

A possible aerodynamic cause could be ice on the back side of the front end core engine compressor blades, we don't know if this crew, or the BA38 crew, even had the engine anti-ice system "on" ?

Even if they had it "on" it does not work when power is at idle from top of descent (as was the case with BA38) to 2000 or 600 feet.

This kind of ice can/will cause the engines to "hesitate" but will long be gone,
when you start looking for it, if the airport temperature is well above freezing.

AAIBs conclusion, that (birds and) ice are ruled out, is way premature.

Read more about engine icing here: www.whistleblowers.dk

Enjoy your reading and thinking.

[AnthonyGA]

If these two incidents are indeed as described, it sounds like a software problem. A mechanical problem would not show coincidentally and abruptly like this after years of presumably trouble-free operation, since the mechanical parts and designs of engines remain unchanged for relatively long periods. Software, on the other hand, is updated much more frequently, and if a recent update contained a bug …

[cribble]

Oluf
In my (Trent powered) 777s the norm is for engine anti-ice to be in "Auto" (I assume other operators do it similarly?): when the ice detection system decrees, the A/I valves are commanded open or closed.

MEL aside, "on" is normally only used on the ground, when conditions dictate.

Even if, in an idle descent, there is not enough bleed air from the LP bleed, there is always the HP bleed- that is, pretty much, why it is there. Even if HP bleed were not enough, when the A/I valves are commanded open the EECs command "approach idle" and a good bit more bleed air is available. So no problem with lack of bleed air for engine A/I in a descent, I think.

Having said that, there is an FCOM caution to avoid prolonged operation in moderate or severe icing conditions.

[Oluf Husted]

Moderate to Severe Icing

Dear Cribble.

Thanks for your technical "run down" on your TRENT-engine!

The wx. during app. of BA38 was in broken clouds with a ground temperature of 11 degrees C. that gives a possible severe icing, since: "The higher the temperature the more severe is the icing condition in 100% humid air" (up to plus 10 degrees C.)

How was the wx. at Los Angeles, where American Airlines had "hesitation" in a Trent?

And according to the latest Norwegian research, by meteorologist Aasmund Rabbe, freezing rain is far more dangerous to jet engines than freezing fog, (by factor 100) due to droplet size, this leaves the FAA AD from 23. jan. 2008 send out to: "Avoid engine failures on short final" in need to explain: "Why the reduction from 1000m to 300m in freezing precipitation, during ground operation (before "run-ups" shall be performed) can be a "tool" to have less (all) engine failures on short final"

Engine anti-ice procedures should be stressed and improved or Boeing 777s with RR engines grounded until a better reason is found.

[sky9]

Even if, in an idle descent, there is not enough bleed air from the LP bleed, there is always the HP bleed- that is, pretty much, why it is there. Even if HP bleed were not enough, when the A/I valves are commanded open the EECs command "approach idle" and a good bit more bleed air is available. So no problem with lack of bleed air for engine A/I in a descent, I think.

Cribble

When I used to fly 757's (RB211) I was amazed at the number of times that I had to fault the failure of the HP valve to open on descent. I had the reputation with the engineers for snagging the valves more than the rest of the pilot force combined. On the 757 there was no eicas message, is there one on the 777?

[BusyB]

Cribble,

The SOP in at least one other Airline is to change from "auto" to "on" on entering icing conditions and back to "auto" on leaving them.

[ACMS]

At CX on the 777 we have been running the Eng Anti-ice manually for the last 6 + years.

Auto is a backup only.

[av8tor94]

NAI

As a long time cold weather operator (Canadian eh) and colleague for years (read decades) of Scandinavian, US and European pilots the accepted practice is to use the AUTO feature only as a backup. System selected on before entering known icing consitions. Maybe that's why it is called Nacelle ANI Ice; wings are a different story of course.

[Oluf Husted]

Captain Nut and Engine Ice

When a student at Cranfields Institute of Technology, named Javid Karim, conducted: "An Investigation Of Aircraft Accidents And Incidents Attributed To Icing, And Cold Weather Operations" among 60 major airlines, he concluded (sep. 1995):

"There is a general lack of crew awareness and training concerning winter operations"

I think, that this is still valid and can tell about my airlines AOM, on the DC9 stated: "Idle power is sufficient" (For engine anti-ice operations on ground and when airborne) this was also valid for the MD80 until 1990, then the procedure was sharpened to: "You SHALL do "run-ups" at least just before T/O and once every teen minutes, to as high a power setting for at least 15 sec. (min. 70% N1) also during taxiing in"

It seems, that only a few pilots and in the Cranfield Study only one of sixty airlines, namely Finnair, take "winter" (all year) operations seriously enough. P & W did not warn their customers before sep. 1994, at least 30 years late!!

Lets hear more experiences about engines "hesitating" and "stalling" on ground and when airborne.

Read more about this on: www.whistleblowers.dk

[ppppilot]

Severe Icing is very usual during winter at Geneve. It has a very high MSA and they are used to make you holding high, close to the Montblanc on intense traffic. Holding at -20º into the rain is severe icing and we used to deploy some spoiler and increase the power since one our pilots declared emergency because of the high vibrations. Vibrations were not only high, were mighty. 11º at surface and just a layer of clouds it is not enough to be guilty and the records don’t appoint that way on the BA38.
Sky9 I have flown a B757 RB211 with the same problem as yours. Changing from IP to HP as the engine reduced to idle, there was a synchronization fault and that produced a stall at the compressor inlet with a strong explosion and a yaw push. The explosion indicates that the flame was out for a while. In such a case, even being a very small stall the recorded parameters must show it.
Same explanation can apply to aerodynamics due to AOA.
Don’t forget that all the records showed normal operation. At least if Boeing has shown all the data in its pocket.¿?

[lomapaseo]

I sense that this thread is straying far afield from the original subject title.

This is not the place to discuss weather and icing issues beyond what is stated in FCOMs. Perhaps a new general thread in the technical section might suffice.

Just to illustrate the complexitity of the discussion

Icing can cause engine problems due to probe blockage; or accretion and sheds resulting in damage; or vibration from uneven sheds; or sheds which mometarily disrupt the airflow.

Simply citing icing as a speculative cause without relating specific factual support applicable for an incident under discussion is like looking for a red herring.

[Orestes]

Aero causes?

Sorry if my earlier comment caused the thread to stray - I was just wondering about other possible causes for a lack of throttle response. I hadn't thought of the possibility of icing issue. Instead, I was wondering if a slow/sticky variable stator vane actuation system in the engine compressor might be a possible culprit.

Anyway, this is all just speculation in the absence of info. I guess we'll just have to be patient and wait for the results of the investigations to find out what's really going on.

[petermcleland]

Orestes...

I asked in the BA thread is it was possible that the compressors were stalled due to high AOA and mentioned that the TGT/JPT would be excessive in that case with failure to produce thrust but lots of noise! I was concerned about several ground witnesses mentioning unusally loud noises from the engines.

I don't think I have ever had compressors stall in an airliner (except possibly those loud bangs on the ground roll with reverse thrust), but I certainly did in a jet fighter with a Rolls Royce Avon engine.

I felt sure that the recorders would show excessive TGT/JPTs in this case but nobody but you seems to have mentioned compressors at high AOA.

Anyway, my post was immediately removed so nobody saw it and replied

[ChristiaanJ]

Peter...
Do you mean aircraft AoA or compressor blade AoA as Orestes says?

If aircraft AoA, you'd be putting the cart before the horse.... the high aircraft AoA happened after the engine problem, as they were trying to drag her over the fence.

[petermcleland]

Yes, I meant aircraft AOA but I meant later in the flight as coming over the road with the engines making an unusually loud noise. The aircraft AOA was certainly high then and I was wondering if the blades were stalled at that time and preventing any increase in thrust. The throttles would have been manually set hard open then, but to no avail.

[bill_s]

What's being posited here is some compressor flow degradation short of the classic compressor stall, where laminar flow collapses violently, with backwards flow due to the instantaneous combustion pressure.

Compressor degradation without total collapse, and with unimpaired fuel flow, should yield lots of smoke - has this been noted in any of these incidents?

[gas path]

BA038

From the QAR/DFDR both engines were 'right on the money' with regard to n1, n2, n3, vane position and bleeds.

[Halfnut]

Thursday afternoon, a B777, aircraft 7BH, en route from MIA to LAX, descended at flight idle power on the profile descent into LAX. At approximately 2000 feet, slowing to 170kts, the autothrottles moved forward to maintain the selected airspeed. The right engine responded normally, but the left engine remained at flight idle for approximately 10-15 secs. The left engine then responded to the demand for increased thrust. The rest of the flight continued with normal engine operation and the flight landed without incident. The aircraft was taken out of service and has been moved to a hangar for further inspection. In light of the recent events at British Airways, we have placed the highest priority on this investigation. Representatives from Boeing and Rolls Royce will participate. We will keep you informed of our findings.

-- Initial review of DFDR data by Rolls Royce indicates a very different event than what British Airways experienced. There were a number of markers in the BA event that are not present In our DFDR data. As it is a concerning event you will be kept informed as more details become available.

-- Boeing, Rolls Royce, AA Maintenance, TAESL Engineering and Flight Test have been unable to uncover any mechanical discrepancies which may have caused the left engines delayed thrust during approach into LAX. All parties reviewed DFDR data and performed extensive fuel and systems testing. At the time the left engine thrust failed to advance, the First Officer (PF) had the speedbrake extended slowing the aircraft from 220kts to 170kts, descending through approximately 3000ft. The DFDR data, which measures actual throttle angle, indicated the left throttle was at or near flight idle while the right throttle advanced.

The only theory that we could prove, which was done in the simulator and again during flight test on Saturday, was the possibility the First Officer may have had his left hand resting on the left throttle for leverage while holding the speedbrake extended, slightly impeding the forward movement of the throttle. Tests on both throttles during flight indicated 1.5 pounds of pressure was required to keep each throttle from advancing. With the left hand on top of the throttle, maintaining back pressure on the speedbrake handle and focused on a very demanding approach, the opposite throttle could advance to maintain airspeed momentarily unnoticed by the crew until a yaw was experienced from differential thrust. The TAC system and autopilot compensation with rudder makes the onset almost unnoticeable. Timed from RT throttle advancement, immediate recognition by the crew, to left throttle awakening and advancing to join the right throttle approximately 12 secs elapsed.

During 2.9 hours of flight test with 2 TUL flight test pilots, the Fleet Captain, and TAESL and Rolls Royce engineers all autothrottle functions and protections worked properly. Minus an unknown mechanical malfunction this scenario was the only plausible way we could recreate this event to match what the crew experienced and what the DFDR data and testing indicated at the time of the event.

This crew did a fabulous job handling this situation and we appreciate their cooperation in this investigation. We certainly are not placing blame, just attempting to explain a scenario that may have produced this set of observed and recorded circumstances.