[jhb_airlines] Re: Standard Procedure

  • From: Gerry Winskill <gwinsk@xxxxxxx>
  • To: jhb_airlines@xxxxxxxxxxxxx
  • Date: Tue, 25 Oct 2005 08:58:18 +0100

So, are the few surviving push pull types intrinsically more safe?

The CAA, apart from ongoing efforts to kill off GA by legislation, seem to take no worthwhile action to eliminate one major killer; car icing.
When they've identified its disaster potential so often, how can they continue to certify any carburetter equipped GA engines. For new a/c I would have thought fuel injection would, by now, be mandatory.

Gerry Winskill

Bones wrote:

The bank should be applied to all engine failure cases as it is related to
the adverse yaw caused by the failed engine. The critical engine isn't
relevant here - but it is highly relevant in the case of pilot limitation.
If the critical engine has failed then the yaw is greater (and the rudder
force needed to contain this is the higher). This will put a severe load on
your leg in trying to keep the aircraft straight and it is likely that you
won't be able to contain it very long. Personally I try to lock my knee over
centre so that it is bone rather than muscle trying to take the strain but I
recall one flight when I could feel it was going to give - and I know I
could not have done anything to stop it. Not a pleasant feeling.

The warning about not turning towards the dead engine is a little more
flexible in that, if really necessary, you could do this but only very, very
gentle turns only. It is far too easy for the aircraft to slip into a spiral
dive in this situation so its really not recommended.

One point I'd like to make is based on my own observations and I must add
that it's not part of any official thinking. You may agree or disagree as
you wish - I add it out of interest.

Engine failures in twins are very serious matters and the track record of
survivability isn't good. It's true to say that many accidents in the past
have started off with an engine losing power (or partially failing) and with
the aircraft going into the deck a few moments afterwards. In my research
through many such cases a pattern emerged that showed the cause of the
accident was not the engine failure itself but loss of control of the
aircraft following the failure. Most post impact investigations showed one
engine running at max power and the other producing little thrust.

We all know the golden rule nowadays is that flying the aircraft is the
first priority in any situation. Too many perfectly sound aircraft have
flown into mountains or the ground because of distraction with others tasks.
This is horribly apt for twins because an engine failure needs immediate
cockpit action to correct the problem - if you don't do them fast enough the
unfeathered prop is going to end the flight very quickly indeed (and I can
assure you that it's bad enough when the prop actually IS feathered).

The trouble is that just after take off you don't have enough time. Lose an
engine and things can go pear shaped in seconds if you don't go through the
drills fast enough. You MUST get the yaw contained immediately (and at Vmca
absolutely full rudder is required) and you MUST get the dead engine's prop
feathered. All the training is concentrated on getting those drills done as
quickly as possible and you practise this again and again and again. Anyone
spot the trap this leads people in to?

In fact there are three traps and I've known good people (some were good
friends) who have been caught out by all of them.

Trap one is the need for speed. Go through the drills as fast as possible as
it is essential to get that prop feathered before the oil cools too much in
the governor. This means you don't have much time to identify the failed
engine - and people have got this wrong. This has caused a few accidents but
isn't the prime killer.

Trap two is the mindset caused by the training. The focus is on getting the
aircraft into a flyable state as quickly as possible by containing yaw and
securing the engine. This diverts you from flying the aircraft and it is
here that most people get killed - they let the aircraft get away from them.
Far too many aircraft are out of control when they hit the ground as pilots
struggle to contain the failure.

Trap three is associated with the above. Because all the training is
dedicated to securing the dead engine and keep the aircraft in a flyable
state pilots don't consider the alternative.

Consider the condition right after engine failure. First the aircraft is
yawing rapidly owing to power differential plus the huge amount of drag from
a windmilling engine. In this state it is not going to stay in the air -
full stop. No aircraft can stay airborne with an unfeathered prop as the
drag is just too much. Full rudder is needed to contain the yaw (the
aerodynamic problem) but then the pilot has to take his eyes away from the
windscreen to sort out the engine problem and get it feathered.

It is here that the accident sequence really begins because once your
eyesight moves away from the windscreen you have lost any clues as to how
the aircraft is behaving. You won't notice that yaw or roll has begun again
and it only needs a second or two to put the aircraft in a non recoverable
state. By the time you look up again it may already be too late.

The sole reason for loss of control is lack of visual perception - the
aircraft is entering a non recoverable position because you are too busy to
see it happening. You can't help this as you have to get the engine
feathered - but with the aircraft on the edge of the flight envelope with
full rudder needed this is the worst moment to be looking away.

What if you took the yaw problem away so that you could sort the engine out
without fear of losing control? Without yaw the aircraft would be stable
enough to give you the few seconds you need with your head inside to sort
the controls out.

I wonder how many twin pilots would actually think about reducing power on
the live engine? To me the loss of control is directly attributable to the
forces produced by the live engine running at full power.

Yep - it sure depends on height but the truth is that if you are so low that
you can't get the prop feathered anyway then you are still going to be
facing a forced landing. A twin with both engines closed is far more flyable
than one with asymmetric power.

If you are a little bit higher then you'd go for the shutdown routine. To
really be safe though you would have to look outside a few times whilst
securing the engine to ensure the aircraft wasn't getting into a dangerous
attitude. This is difficult with both full rudder applied and your attention
then diverted on the shutdown routine and pulling all the right levers.
Until all this is done the aircraft is still going downhill.

If you pulled the power back on the live engine then the rate of descent
will increase - but not by a lot. You wouldn't have to apply anything like
full rudder and the aircraft would be far more stable - it wouldn't be half
as critical to take your eyes inside to sort out the engine.

Just my own thoughts.

As to the big tin I'm sure they mostly do their engine failure cases in the
sim these days. For live training I suspect they could still partly simulate
an engine failure by bring back one engine to neutral thrust but this
wouldn't be of any value except for handling purposes (maybe useful during
an hold or ILS procedure to see what the pilot does). It wouldn't produce
all the system failures had the engine fully quit.


-----Original Message-----
From: jhb_airlines-bounce@xxxxxxxxxxxxx
[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Peter Dodds
Sent: 24 October 2005 15:46
To: jhb_airlines@xxxxxxxxxxxxx
Cc: pdodds@xxxxxxxxxxxx
Subject: [jhb_airlines] Re: Standard Pocedure

Very interesting, John (as always). I knew a bit about flying twins in the circuit, because I remember a friend of mine doing a twin rating. He never mentioned not turning towrds the dead engine, nor flying with 5 degrees of bank - he was flying a Baron which has contra-rotating props, so no critical engine. Would that have been a factor why he never mentioned it? (apart from simply being too knackered for his brain to function properly after his lessons).

He had to fly whole circuits with no rudder trim - 2 or 3 one
after the other.  He almost limped into the club house
afterwards, white as a sheet. He also said there was a "pilot
limited" assymetric speed, personal to each pilot.  I can't
remember whether this was an approach speed, climb speed or
cruise speed, but it was all to do with how much push he could
maintain with his leg on the rudders. This critical speed was the
speed at which the rudder forces were less than or equal to the
amount of push he could maintain with his leg!

I don't think he ever flew twins seriously!

Presumably this type of assymetric flying isn't possible with
servo actuated controls in the big tin??


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