The turbine engine might warn you that it is about to fail

[pelmet]

While I have had quite a few shutdowns of turbine engines over the years, they were mostly precautionary, a flameout or due to a propeller issue.
But there was one actual complete mechanical failure quite a long time ago and we were give a very subtle warning. We taxied out for departure and at the end of the runway, the captain said "do you feel that?". At first I didn't but when he mentioned a vibration in the seat, I did feel and hear it. All other indications seemed normal and we took off. It was actually at a fairly nasty airport to have an engine failure so we were fortunate that it autofeathered on descent. Once on the ground, the prop was seized and some bits of molten metal that had hardened could be seen in the exhaust area.


I was reminded of that event recently when I read an article that my company had provided about engine failures.....

"A high N1 vibration level may be accompanied by perceivable airframe vibration.
A sudden increase of the vibration level indicates a possible deterioration of the engine. During takeoff, the vibration indication should be stabilized once takeoff thrust is set. If the advisory threshold is reached, a low speed rejected takeoff may be considered. The vibrations should not vary significantly during the takeoff roll. If it suddenly increases significantly, a rejected takeoff should be considered depending on the circumstances."

http://www.smartcockpit.com/docs/Handli ... ctions.pdf

By coincidence, I also read this incident report on the same day....

"C-GSCA, a Boeing 767-300 aircraft operated by Air Canada rouge, was conducting flight
ROU1901 from Athens/Eleftherios Venizelos Intl (LGAV), Greece to Toronto/Lester B. Pearson Intl
(CYYZ), ON with 9 crew members and 189 passengers on board. Upon selection of initial thrust at
the start of the takeoff phase on Runway 21L, the flight crew noted a slight yaw. As the engines
spooled up to the selected thrust setting, an abnormal rumbling noise could be heard. Passing 80
KIAS, the right engine (General Electric CF6-80C2B6F) began to roll back and was unresponsive
to thrust commands. The takeoff was rejected at 110 KIAS, the aircraft stopped on the runway and
became disabled as 2 outboard main landing gear tires had blown. The flight crew declared a PAN
PAN, and ARFF attended to the aircraft."

Each real world event was slightly different than what the article stated but that seems to be the way it is with most malfunctions, few of which are exactly the same as the written aircraft manual. But I think it shows that one might want to consider an alternative to taking off if the engine is giving you a subtle warning.

[digits_]

I agree with the link between engine vibrations and engine health. The problem lies in identifying a vibration as an engine vibration. Could be a generator, ice, prop issue, aerodynamic vibration or a plethora of other things.
That makes a faint vibration a bit of a, dare I say, useless diagnostic tool in many situations.

[pelmet]

Good points about the difficulties faced by the pilot when trying to make a diagnosis.

Most of the examples are likely to be airborne events. The article does say.....

"Vibrations alone should not lead to an in-flight shutdown. "

[complexintentions]

Each real world event was slightly different than what the article stated but that seems to be the way it is with most malfunctions, few of which are exactly the same as the written aircraft manual. But I think it shows that one might want to consider an alternative to taking off if the engine is giving you a subtle warning.

I can agree that one should always pay attention to what their equipment is telling them, but the takeoff roll is precisely NOT the time to be analyzing "subtle warnings". The whole procedure is designed for completely the opposite, to nearly entirely remove decision-making during that phase. With good reason.

If something is troubling you during the start-up/taxi out, by all means investigate. But offering a rejected takeoff as an example scenario could be giving less experienced readers exactly the wrong idea. The Rouge flight didn't reject because of anything subtle, they rejected because they had an engine failure prior to V1.

The thing is, even in your own example, if you had declined the flight because of the slight vibration, what justification could you give? The fact that in this one case a vibration presaged a failure does not mean that it would in another. The system worked exactly as designed - a failure occurred and was covered by redundant design.

Even inflight, trying to out-think a modern aircraft and its designers has to be done with extreme caution. The days of knowing the consequences of every action if you take it on yourself to start troubleshooting outside of published procedures are long gone.

[pelmet]

Each real world event was slightly different than what the article stated but that seems to be the way it is with most malfunctions, few of which are exactly the same as the written aircraft manual. But I think it shows that one might want to consider an alternative to taking off if the engine is giving you a subtle warning.

I can agree that one should always pay attention to what their equipment is telling them, but the takeoff roll is precisely NOT the time to be analyzing "subtle warnings". The whole procedure is designed for completely the opposite, to nearly entirely remove decision-making during that phase. With good reason.

If something is troubling you during the start-up/taxi out, by all means investigate. But offering a rejected takeoff as an example scenario could be giving less experienced readers exactly the wrong idea. The Rouge flight didn't reject because of anything subtle, they rejected because they had an engine failure prior to V1.

Thanks for the reply,

I understand the reasoning of your statement, but I am not sure I agree with the idea decision-making being nearly entirely removed during the takeoff roll. In fact, I think during the initial stages of the takeoff roll(below 80 knots for the airliner types and certainly when just setting the takeoff thrust), the pilot should be making decisions on whether or not an RTO should be made for a multitude of reasons, which can prevent a dangerous high speed RTO.

While I definitely think that one should be go-minded in the higher speed ranges, I also think that one should be stop-minded in the low speed range.

In this case, warning signs were given early, potentially allowing for an RTO well below 110 knots.

It was actually at a fairly nasty airport to have an engine failure so we were fortunate that it autofeathered on descent.

The thing is, even in your own example, if you had declined the flight because of the slight vibration, what justification could you give? The fact that in this one case a vibration presaged a failure does not mean that it would in another. The system worked exactly as designed - a failure occurred and was covered by redundant design.

I agree that there was no real reason at the time to not takeoff, but the system almost did not work. It was the riskiest of all airports we flew at when taking off in the direction we did. It had an engine out procedure that started at 50 feet requiring a 180 degree turn and solid mountain close in which had to be avoided by ensuring a reasonable turn radius combined with an underpowered aircraft.

It happened to be daytime and the reality is that if there had been an engine failure at V1 or soon after, we would have ignored the engine out procedure and turned left instead of right on a better route. But at night, one had to do the engine-out procedure. I always figured that if the worst case scenario happened(the failed engine pulling one away from the required turn) one would never make it. Anyways, our failure didn't happen during the takeoff and we climbed out through the mountains enjoying the scenery with our about to fail engine.