EFATO Light Twin/ Mixture Control.
Joined: Jun 2000
Aviation Qualifications: ATP+Mil
Posts: 4,697
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From: Australia
CC.
Dead right and in fact some years ago Mac Job the well known flight safety aviation writer made exactly the same point as you have - that is light twin engine safety is tied to cost.
That is the bottom line in my view...cost...the overall statistics suggest that any increased safety of one over the other is really to vague to actually quantify with any certainty. That is a shame because it should be a no brainer...I guess the no brainers are to blame.
Joined: Mar 2006
Posts: 78
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From: Australia
Always an interesting subject.
It is rubbish to suggest that it is more kind to the engine by cutting the mixture, as maui does here:
The two methods of simulating the failure are in fact, almost identical (from the power loss point of view). Both rapidly deprive the engine of the heat energy that would be converted to mechanical energy. Following the loss of power, you have the situation that is referred to in numerous different ways by pilots, but which all mean exactly the same thing:
- "Windmilling"
- "Backdriving"
- "Backloading"
- "Negative torque"
Chimbu said:
Sadly, I have to agree with this. 8 children lost their fathers a few years ago at Jandakot because the pilot, having lost an engine just after takeoff, was in too much of a hurry to get the aircraft back onto the ground. The aircraft was maintaining height (albeit very low) at speeds around the blue line but a steepish turn when attempting to get back to the runway took the aircraft too far back on the power curve and a collision with the ground (and fireball) was the inevitable result.
The significance of NOT TURNING when assymetric is nowhere near emphasised enough. It should be hammered into multi pilots as much as the "don't turn back" message is hammered into single pilots for when they lose their engine just after takeoff.
On this point, the opinion of Chimbu was:
On VYSE: too many pilots have too much regard for this number when considering a multiengine takeoff. It is revered as an almost magical number that determines whether you will be able to fly or not. Too many pilots have the view that "if you lose one before blueline you won't climb".
That view is rubbish and pilots that hold it are firmly in the moron category that Chimbu referred to earlier. If you are one of them I ask you: what about VXSE? That speed is always less than VYSE (by almost 10 knots in the case of one type) and because of the relationship between these speeds, if you can climb at one, you will climb at the other - and if you can't climb at one, you won't be able to climb at the other.
Readers of this post may be interested to know that the blue line is NOT marked on the ASI to assist pilots in the EFATO case. When the FAA mandated the blue line in the early 60's it was for the case where the aircraft lost one in the cruise.
Centaurus is right on with this comment about blue line:
Finally, hands up all those whose drill, following an engine failure after takeoff with flaps extended, is to retract the flaps immediately after retracting the gear? (As part of the drill, in other words).
If you put your hand up then I suggest you read the manufacturers instructions re engine failures after takeoff - you may find that the POH stipulates that you leave the flaps alone - until reaching a "safe height".
The POH for a Cessna 400 series type stipulates exactly this - but how many of us have been trained to follow the "mixture up, pitch up, power up, gear up, flaps up" drill?
It is rubbish to suggest that it is more kind to the engine by cutting the mixture, as maui does here:
Conventional wisdom in the past was that a mixture cut was easier on the engine as the loading stays positive. If the throttle is pulled abruptly backloading occurs, which can do nasty things to dynamic balances. Additionally if the engine is of the geared variety the lay shafts take a caning.
- "Windmilling"
- "Backdriving"
- "Backloading"
- "Negative torque"
Chimbu said:
Morons have caused piston twins to have the reputation they have not the aircraft themselves.
The significance of NOT TURNING when assymetric is nowhere near emphasised enough. It should be hammered into multi pilots as much as the "don't turn back" message is hammered into single pilots for when they lose their engine just after takeoff.
On this point, the opinion of Chimbu was:
Climb in a straight line and get at least 4-500' under you before you even think about turning....yes if there is a hill in front miss it
That view is rubbish and pilots that hold it are firmly in the moron category that Chimbu referred to earlier. If you are one of them I ask you: what about VXSE? That speed is always less than VYSE (by almost 10 knots in the case of one type) and because of the relationship between these speeds, if you can climb at one, you will climb at the other - and if you can't climb at one, you won't be able to climb at the other.
Readers of this post may be interested to know that the blue line is NOT marked on the ASI to assist pilots in the EFATO case. When the FAA mandated the blue line in the early 60's it was for the case where the aircraft lost one in the cruise.
Centaurus is right on with this comment about blue line:
Blue line is a meaningless figure as a decision figure. It is best single engine rate of climb and no more than that. It is not a decision speed quoted in any manufacturer's POH. Lose an engine in a Seminole 5 knots above the blue line of 88 knots and you will be unpleasantly surprised how quickly you have done in 10 knots below blue line due to the drag of the failed engine.
If you put your hand up then I suggest you read the manufacturers instructions re engine failures after takeoff - you may find that the POH stipulates that you leave the flaps alone - until reaching a "safe height".
The POH for a Cessna 400 series type stipulates exactly this - but how many of us have been trained to follow the "mixture up, pitch up, power up, gear up, flaps up" drill?
Joined: Dec 2001
Aviation Qualifications: ATPL
Posts: 4,419
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From: Brisvegas
From the Beechcraft Baron 58 POH P/N 58-590000-39 Issue Oct 1984 revised October 1990.
Page 3-5.
ENGINE FAILURE AFTER LIFT-OFF AND IN FLIGHT.
1. Landing Gear and Flaps - UP
2. Throttle (inoperative engine) -CLOSED
3. Propeller (inoperative engine) - FEATHER
4. Power (operative engine) - AS REQUIRED
5. Airspeed - MAINTAIN SPEED AT ENGINE FAILURE (100 kts MAX) until OBSTACLES ARE CLEARED
...checklist then goes on to talk about securing failed engine.
Interesting that the manufacturer advocates flap up at step 1 but does not talk about clearing obstacles and increasing speed until step 5.
The "five ups" are not perfect but they work most of the time.
Page 3-5.
ENGINE FAILURE AFTER LIFT-OFF AND IN FLIGHT.
1. Landing Gear and Flaps - UP
2. Throttle (inoperative engine) -CLOSED
3. Propeller (inoperative engine) - FEATHER
4. Power (operative engine) - AS REQUIRED
5. Airspeed - MAINTAIN SPEED AT ENGINE FAILURE (100 kts MAX) until OBSTACLES ARE CLEARED
...checklist then goes on to talk about securing failed engine.
Interesting that the manufacturer advocates flap up at step 1 but does not talk about clearing obstacles and increasing speed until step 5.
The "five ups" are not perfect but they work most of the time.
Joined: Mar 2006
Posts: 48
Likes: 0
From: Sydney
cc said
and
i must respectfully disagree. IMHO you should fly at Vy (Vx for obstacle clearance if necessary). that provides the highest altitude should you suffer an engine failure. you must remember that drag is proportional to the square of the airspeed so the higher the speed, the quicker you will slow down anyway. much better to be at 400' at 85kts then 250' at 100kts in something like a duchess when the engine stops.
RAAF procedures are as i describe and it certainly is the beechcraft recommendation.
Accelerate in a VERY gentle climb to at least Vyse+10kts. Note I am NOT advocating flying level at 2'!!!
Climb out at Vyse+10-20kts or cruise climb. Speed is ESSENTIAL not altitude. DO NOT reduce power to some BS 25/25 setting...leave everything all the way forward.
At the higher speed you'll need less rudder to control yaw and you have 'ample' time to carry out the memory items and assess whether the aeroplane will actually climb away and allow a circuit and landing while you gently raise the nose and climb with the speed VERY gently reducing to Vyse
At the higher speed you'll need less rudder to control yaw and you have 'ample' time to carry out the memory items and assess whether the aeroplane will actually climb away and allow a circuit and landing while you gently raise the nose and climb with the speed VERY gently reducing to Vyse
RAAF procedures are as i describe and it certainly is the beechcraft recommendation.
Joined: Jun 2001
Posts: 889
Likes: 0
From: Australia
IMHO you should fly at Vy (Vx for obstacle clearance if necessary). that provides the highest altitude should you suffer an engine failure.
If I have an obstacle to clear, then I will maintain Vy or Vx until a safe height, as per manufacturer's recommendation. But I specifically remind myself that I'll need to lower the nose dramatically in the event of an EF. This will also necessitate turning early or landing ahead because I won't clear the obstacle. Not a "normal" take-off (for me at least!)
I too am interested in whether it damages the engine to apply mixture ICO -> fully rich with the throttle open. It's a pity no-one seems to know.
Thanks to all the very experienced pilots who have made posts here - CC & Centaurus among others. I (we?) have appreciated your taking time to pass on your knowledge.
Grandpa Aerotart
Joined: Jun 2000
Posts: 4,579
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From: SWP
wdn Vy and Vx are certification speeds (test pilot territory) not really applicable in day to day flying. They were speeds born of some certification requirement and have, like so many things in aviation, taken on a life of their own.
Think about it. A 50' obstacle exactly at the end of the TODA.
Think also about how low 50' is.
You'll be above 50' before the gear is up.
And yet we see pilot after pilot climbing away at Vy to some truly stupid altitudes...500'-1000' or even cruise altitude as often as not...cruise climb seems to be a mystery to many pilots.
It is, in my view, negatively reinforced by the diagrams you see depicting Vy/Vx in sundry publications. Usually a picture of a cessna standing on it's tail climbing over a tree....the scale errors of the diagram make it look like the tree is actually several hundred feet high and that, I suspect, is the psycological factor which starts pilots climbing at Vy to such completely stupid altitudes.
In my Bonanza Vy is 93 kts. Glide speed in the landing config is 90kts and glide speed clean is 110kts. At 93 kts the nose is hauled up so high that the view ahead is severely compromised. If you lose an engine in that attitude you'll be below 90ts in a heart beat and have to lower the nose dramatically in an attempt to get it back let alone 110kts. At an altitude of say 100' you will merely develope a very high rate of descent without the time to recover speed and its attendant manouever capability. You will then be faced with the ground arriving to smite thee in the face at some horrifying rate and a almost guaranteed very heavy arrival.
In a twin many of the same considerations apply but for slightly modified reasons. If you are climbing away in a typical piston twin at Vy in an effort to get lots of altitude 'quickly' in case of engine failure and you actually lose an engine you will need LOTS of rudder to control the yaw and need to lower the attitude dramatically to;
1/. stop further speed decay,
2/. regain a speed which will allow you to climb/maintain height while you sort !!!! out.
Given the extremely high oh !!!!!!! factor in typical real engine failures this is beyond the capabilities of many pilots and, in my view, is exactly how Vmca loss of control accidents happen.
In my Bonanza I get airborne, gear up, gently climb/accelerate to 110Kt asap. If I lose the engine at any point I need only to lower the nose slightly to maintain speed and look for something soft to hit. Once I actually have 110Kts the aeroplane is truly manoueverable and can look at turning left or right slightly for better opportunities if they exist. At 110kts my wing really comes alive and I get initial climb rates of 1000'/min at 110-120kts...with nice cool CHTs as well
The same applied when I used to fly Barons etc. Accelerate in a gentle climb looking for that cruise climb 'sweet spot' and if you lose an engine you have a nice buffer above Vyse (and that may not be the blue radial painted on the ASI. Control initial yaw with rudder (you'll need a lot less at the higher IAS) gently lower the nose a small amount to maintain speed and carryout the recall items- mixture/pitch/power up, wheel ups/flaps up/ identify, verify, feather, fuel.
I have yet to see an airport/airstrip in my career that required Vy/Vx
Editted for spooling...again.
Think about it. A 50' obstacle exactly at the end of the TODA.
Think also about how low 50' is.
You'll be above 50' before the gear is up.
And yet we see pilot after pilot climbing away at Vy to some truly stupid altitudes...500'-1000' or even cruise altitude as often as not...cruise climb seems to be a mystery to many pilots.
It is, in my view, negatively reinforced by the diagrams you see depicting Vy/Vx in sundry publications. Usually a picture of a cessna standing on it's tail climbing over a tree....the scale errors of the diagram make it look like the tree is actually several hundred feet high and that, I suspect, is the psycological factor which starts pilots climbing at Vy to such completely stupid altitudes.
In my Bonanza Vy is 93 kts. Glide speed in the landing config is 90kts and glide speed clean is 110kts. At 93 kts the nose is hauled up so high that the view ahead is severely compromised. If you lose an engine in that attitude you'll be below 90ts in a heart beat and have to lower the nose dramatically in an attempt to get it back let alone 110kts. At an altitude of say 100' you will merely develope a very high rate of descent without the time to recover speed and its attendant manouever capability. You will then be faced with the ground arriving to smite thee in the face at some horrifying rate and a almost guaranteed very heavy arrival.
In a twin many of the same considerations apply but for slightly modified reasons. If you are climbing away in a typical piston twin at Vy in an effort to get lots of altitude 'quickly' in case of engine failure and you actually lose an engine you will need LOTS of rudder to control the yaw and need to lower the attitude dramatically to;
1/. stop further speed decay,
2/. regain a speed which will allow you to climb/maintain height while you sort !!!! out.
Given the extremely high oh !!!!!!! factor in typical real engine failures this is beyond the capabilities of many pilots and, in my view, is exactly how Vmca loss of control accidents happen.
In my Bonanza I get airborne, gear up, gently climb/accelerate to 110Kt asap. If I lose the engine at any point I need only to lower the nose slightly to maintain speed and look for something soft to hit. Once I actually have 110Kts the aeroplane is truly manoueverable and can look at turning left or right slightly for better opportunities if they exist. At 110kts my wing really comes alive and I get initial climb rates of 1000'/min at 110-120kts...with nice cool CHTs as well
The same applied when I used to fly Barons etc. Accelerate in a gentle climb looking for that cruise climb 'sweet spot' and if you lose an engine you have a nice buffer above Vyse (and that may not be the blue radial painted on the ASI. Control initial yaw with rudder (you'll need a lot less at the higher IAS) gently lower the nose a small amount to maintain speed and carryout the recall items- mixture/pitch/power up, wheel ups/flaps up/ identify, verify, feather, fuel.
I have yet to see an airport/airstrip in my career that required Vy/Vx
Editted for spooling...again.
Last edited by Chimbu chuckles; 2nd July 2006 at 07:02.
Joined: Jun 2001
Posts: 889
Likes: 0
From: Australia
Yeah. Wot he said.
In my reading of accident reports, most fatalities arising from EFATO in a light twin were completely avoidable. For example - struggling to gain height at Vxse or Vyse, then hitting a hill? Very rare scenario. Another example - aircraft committed to a forced landing, pilot closes both throttles before touchdown? Again, very rarely fatalities from this scenario.
What I have read many cases of, is pilots maintaining an excessive pitch attitude when asymmetric, with a quick speed decay to below their personal Vmc. That almost always results in multiple fatalities. I have seen intelligent and current students do it in training, and had to take over control. Why do people do it? Without having experienced a real EF, I agree it's the "oh bugger" factor, coupled with a psychologically overwhelming desire to climb away at something that looks "normal".
While I agree with your airspeed - life axiom, I consider that there are statistically safer ways to fly a light twin where terrain is not limiting.
In my reading of accident reports, most fatalities arising from EFATO in a light twin were completely avoidable. For example - struggling to gain height at Vxse or Vyse, then hitting a hill? Very rare scenario. Another example - aircraft committed to a forced landing, pilot closes both throttles before touchdown? Again, very rarely fatalities from this scenario.
What I have read many cases of, is pilots maintaining an excessive pitch attitude when asymmetric, with a quick speed decay to below their personal Vmc. That almost always results in multiple fatalities. I have seen intelligent and current students do it in training, and had to take over control. Why do people do it? Without having experienced a real EF, I agree it's the "oh bugger" factor, coupled with a psychologically overwhelming desire to climb away at something that looks "normal".
While I agree with your airspeed - life axiom, I consider that there are statistically safer ways to fly a light twin where terrain is not limiting.
