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Twins - engine failure / EFATO (merged)

Twins – is an engine failure a risk during cruise climb?

I’ve just read this?

One should be climbing at way above the minimum single engine speed, surely?

Administrator
Shoreham EGKA, United Kingdom

The drag from a windmilling prop dominates, so if the pitch attitude is not lowered speed will decay very quickly. If the pilot also reacts instinctively, and not as per training, he may use roll to attempt control. This increases both drag (aileron drag, induced drag on failed engine wing and sideslip drag) and the beta angle on the rudder leading to a departure of control when the rudder stalls, usually when the pilot tries to recover by finally applying rudder input and thereby lowering the critical beta of the rudder due to increased camber.

Maintaining the initial attitude, using roll control to maintain control, will reduce speed from cruise climb towards a departure due to either a Vmc roll or spin entry in probably less than a minute.

Enstone (EGTN), Oxford (EGTK)

And of course, the stronger the engines the less forgiving situation.

LDZA LDVA, Croatia

I have always thought that one failing of OEI training is lack of guidance on how to recognise that you do indeed have an engine failure and not some other problem.

In training you always know a failure is coming, so when you see the aircraft roll uncommanded (you usually notice the roll first, particularly on a big PFD), you immediately think “ooh, engine failure” and go for the rudder.

But in a real world scenario, especially IMC, when you see the aircraft roll and you don’t yet know it’s an engine problem, you may instinctively apply aileron first. Or the AP may do so.

There is little discussion of this in typical MEP training. It focuses instead on dealing with the engine failure on the assumption that you already know that this is indeed the problem.

t focuses instead on dealing with the engine failure on the assumption that you already know that this is indeed the problem.

Same thing with unreliable speed indication, etc. The training is focused on the skill test drills.

Vyse climb has some margin, but depending on type, that marging can be broad or narrow. But unless there’s imminent obstacle clearance issues, I would personally transition to level flight during any engine out scenario to assess problems or troubleshoot rather than sustain a climb. One less axis to worry about.

On the Aerostar the gap between redline and blue line was pretty broad. And it always took a little while to accelerate from rotation up past blue line. The Aerostar was not a good climber before 100kts IAS. Those were always the times where I pushed the nose down a little to narrow that gap as quick as possible. So I’d often rotate, hold the nose down and build speed to above blue line, then climb out. Almost like a short field takeoff where you want to stay in ground effect for longer. I also delayed my rotation to well above red line, just to build extra margin. Thankfully on the Aerostar, the rotation speed was close or above redline. That was not the case on the Commander 520. You could get that flying and climbing out well below redline, which, if you’d ever lose one in that scenario, you’d probably not recover from during a takeoff.

This clip shows a T/O crash due to engine failure


When I was flying multi engines aircraft the rule that was drummed into me never to land or rotate below blue line (if r/w is long enough and aircraft allows).

Recently I thought about a very simple system that will identify engine failure by measuring the engines delta of the manifold pressure, the minute pressure drops it warns the pilot and indicates which engine failed.

I have canvased opinions on a US forum that has relatively large number of M.E pilots who thought that this sort of device will not be useful. As the subject was raised hear I have thought to ask the same question here too.

Thanks

MP is not necessarily a reliable indicator, yaw towards the failed engine is. MP will fluctuate and trends towards ambient pressure as the engine fails.

Enstone (EGTN), Oxford (EGTK)

As is known, I know almost nothing about twins but I have heard many times that the prop governor masks the early mechanical symptoms of an engine failure, by maintaining the RPM in the face of a reduction in torque, and since the entire side of the engine between the air intake and the inlet valves is just an air pump, constant RPM means constant MP (obviously assuming a constant throttle setting).

The only bit which tells you really early something has gone is a multi cylinder EGT gauge.

Well, apart from a piston exiting via the cowling but that would also show up on that cylinder’s EGT right away.

Would not yaw towards the failing engine be initially masked by a yaw damper? Also, especially in IMC, would you not need to be a fairly sharp pilot to notice the ball moving off to one side, slowly?

Administrator
Shoreham EGKA, United Kingdom

http://www.nasa.gov/centers/dryden/pdf/87772main_H-584.pdf

Yaw damper would be off in an EFATO scenario. In cruise climb, and presumably above MSA, you would be fault finding before feathering although the P in the old PAIDOFFSTAR mnemonic stands for Prevent yaw with rudder.

Enstone (EGTN), Oxford (EGTK)
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