CNN: Engine type found on 1549 may run too hot, causing compressor stalls.

[originalpckelly]

They did however, say that they had no reason to believe that this plane was equipped with one. I only caught part of the report, but they said that 3,000 of the engines had been inspected finding only 12 engines with problems.

I don't know about you, but it is starting to sound kind of odd, how this plane had these compressor stalls a few days before it crashed, then had them again the day it crashed, and the engine type is known to have possible problems causing those very same compressor stalls.

Sounds pretty fishy, but maybe it's all a co-incidence. If it is, then CNN is being irresponsible reporting like that, as it implies impropriety on the part of the airline.

[tabatha]

1. Probably it was a marginal engine

that was totally shut down by birds.

[onehandle]

2. Geese hitting at high speed cause more problems than compressor stalls. nt

[originalpckelly]

3. We assume the bangs were from the birds, and not the compressor stalls.

It's not like we can do anything about it, we just have to wait and see what CNN says, since they seem to be fleshing out this story.

And here's a bird stall for proof that even one bird can cause one:
http://www.liveleak.com/view?i=7ae_1183872776

So it seems very plausible it was the birds, on the other hand, perhaps it was a "marginal engine" as said above.

[MajorChode]

6. Chicken/egg

The former can cause the later and is what many are assuming at this point.

The damage caused by bird ingestion can cause or exasperate a compressor stall.

[MajorChode]

4. Compressor stalls are actually reasonably common

Many airlines have had problems with compressor stalls on various airframes, including the same Airbus series as flight 1549. It will be interesting to see the full NTSB report, but that will probably take a year or more.

[originalpckelly]

5. They happen in that engine, in bad ones...

because it runs too hot. Maybe that causes metal fatigue?

[MajorChode]

8. Anything is possible, but I'm not convinced of that scenario

One common reason why compressor stalls happen is because of reduced airflow through the engine. This can happen in severe crosswinds, but generally only affect one engine. In older planes, the pilots would have to reduce fuel flow to a stalled compressor and then slowly bring it back up. Modern engines do this automatically.

There is still a lot of unanswered questions. The NTSB postmortem on the engines should answer a lot of those questions.

[originalpckelly]

10. Computers control these engines don't they?

Wonder if that's the problem? What if they were improperly regulating the fuel flow?

[MajorChode]

12. It is possible

If there were indeed birds ingested, this may have created a problem the computer control wasn't prepared to properly deal with. All of this is just speculation. That's why a thorough investigation is needed.

[DemoTex]

14. That scenario assumes simultaneous catastrophic failure of two independent systems.

It assumes simultaneous catastrophic failure of two independent FADEC (Full Authority Digital Engine Control) systems and, as a result, the subsequent simultaneous catastrophic failure of two independent engines. I'm thinking probabilities in the range of 10-to-the-minus-12th.

But it is possible.

[MajorChode]

15. Well not only that, but

It's my understanding the FADEC systems have at least dual redundancy on each side. However, I'm thinking more along the lines of a scenario that the FADEC designers didn't anticipate, more than just an electrical or mechanical failure of some sort. Again this is all just pure speculation at this point from someone who has little idea about how those systems were actually designed. I have confidence the NTSB will be able to sort it out.

[conscious evolution]

7. I heard a report

that both engines quit at the same moment.
Is this true?
If so,to me,that points at something other than bird fod or compressor stall.What are the odds of both engines dieing at the same moment from either cause?Seems to me it would be a failure of something that both engines rely for that to happen.Something like a problem with the fuel system or the plane engines electrical/electronics components.

[originalpckelly]

9. Agreed, how likely is it that birds hit the engines at the exact same time?

Maybe it's a problem with the computers that control the engines?

[DemoTex]

16. The NTSB investigation will look closely at the FADECs and the fuel system ..

And the elecrical system, and environmental system .. etc, etc. It would be remiss not to.

But you asked: " .. how likely is it that birds hit the engines at the exact same time?"

My answer: Very likely if it was a flock of birds. The Airbus was in level (or gently turning) climbing flight accelerating to the speed limit (below 10,000 ft) of 250 knots. The bird ingestion by the engines (if there were bird strikes) probably happened at virtually (but not exactly at a threshold of, say, 1/100th of a second .. but that is not germane unless we have access to DFDR data) the same instant.

In the incident I cited elsewhere in this thread, the captain of the B-737 at FLL told me that the popping from the seagull strikes and compressor stalls was equally loud and in "stereo" from both sides of the aircraft. That B-737 had wing leading edge damage, engine nacelle damage, flap and slat damage, and landing gear damage on each side that was almost equal in severity and physical distribution. I saw the photos that the captain took when he got back to the gate with his damaged jet and shaken passengers and crew. Obviously, the damage was not totally symmetrical because one CFM-56 continued to develop enough thrust to get the jet around for a safe landing.

[DemoTex]

11. High engine temps do not cause compressor stalls .

But compressor stalls can cause high exhaust or turbine temperatures (EGT, ITT). The EGT and ITT temp sensors are always aft of the compressor section (airflow wise).

Compressor stalls are caused by disruptions in the airflow into the engine. Bird ingestion by an engine might result in compressor stalls, to the point of excessive EGT values and engine flame-out. Severe turbulence can cause compressor stalls (I had a CJ-610 engine on a Learjet 25 flame-out at 45,000 ft in severe turbulence, after warning me first with a few loud compressor stalls). A gusty crosswind on initial takeoff roll (slow speed, high power) can cause compressor stalls (especially on the downwind-side engine).

I have almost 8000 hours flying Boeing 737s with the CFM-56 engine, like the CFM-56-5s that powered flight 1549. I have had bird strikes, severe turbulence, and serious foreign object damage to CFM-56 engines and have never had a compressor stall or flame out.

I am aware of a CFM-56 powered B-737-400 that hit a flock of sea gulls at Ft. Lauderdale right at lift-off a few years ago. One engine ingested so many birds that it flamed-out immediately. The captain flew the fully-loaded, heavily-damaged aircraft (the "good" engine was vibrating and severely damaged, too) around for a tight instrument approach and a successful landing on a runway littered with dead seagulls. He and his first officer received the ALPA "DFC" that year for superior piloting.

http://en.wikipedia.org/wiki/Compressor_stall

[MajorChode]

13. But is comparing the same engine in different airframes valid?

As you say, compressor stalls are caused by disruptions in airflow to the engine, but the A320 engine installation looks considerably different than a 737.