PFL with mixture set to lean
Join Date: Jan 2012
Location: London
Posts: 21
Likes: 0
Received 0 Likes
on
0 Posts
Up untill a few days back I would have thought putting the mixture to idle cut off when doing a PFL was unwise.
But I now have to consider if there is a good reason for this or is the student telling the whole truth so I will leave comment to Those who have far more wisdom, insight and qualification.
But I now have to consider if there is a good reason for this or is the student telling the whole truth so I will leave comment to Those who have far more wisdom, insight and qualification.
Join Date: May 2006
Location: Londonish
Posts: 779
Likes: 0
Received 0 Likes
on
0 Posts
I think it is unusual, but not unheard of. As Genghis says, there's a lot of 'it depends'.
With respect to (ever) being assured of the landing, gliders do it all the time. Essentially you're staying higher than a best glide profile for the whole approach and throwing away the energy late on.
Gliders do it by flying half airbrake (or spoiler), and having the option to open more to descend, or close to essentially 'climb' on the profile.
I've only flown a stopped prop approach once (instructor request) and a lot of idle approaches. The technique is similar - stay high (but not too high) throughout to keep a margin, slip, take flap (or in extremes, S turn) on final to kill energy and (assuming plenty of runway) aim 1/3 into the field, NOT for the numbers. That way a little unplanned sink means taking the flap later, or maybe landing short of your aim point, rather than in the hedge.
If the trees are getting a bit too big you can always cut the corner, and if it's looking really bad land on any available bit of grass, even crosswind. Few a/c in private use are going to fall apart if presented with grass, the runway is not an absolute requirement, and airfields are usually more likely to be obstruction free than the surrounding fields. Rather dramatic for an exercise mind you!
With respect to (ever) being assured of the landing, gliders do it all the time. Essentially you're staying higher than a best glide profile for the whole approach and throwing away the energy late on.
Gliders do it by flying half airbrake (or spoiler), and having the option to open more to descend, or close to essentially 'climb' on the profile.
I've only flown a stopped prop approach once (instructor request) and a lot of idle approaches. The technique is similar - stay high (but not too high) throughout to keep a margin, slip, take flap (or in extremes, S turn) on final to kill energy and (assuming plenty of runway) aim 1/3 into the field, NOT for the numbers. That way a little unplanned sink means taking the flap later, or maybe landing short of your aim point, rather than in the hedge.
If the trees are getting a bit too big you can always cut the corner, and if it's looking really bad land on any available bit of grass, even crosswind. Few a/c in private use are going to fall apart if presented with grass, the runway is not an absolute requirement, and airfields are usually more likely to be obstruction free than the surrounding fields. Rather dramatic for an exercise mind you!
Moderator
My own opinion is that the risk outweighs the benefit of actually stopping the engine of a single at any point. The very small additional "experience" is really not worth the chance of something going wrong, and needing a stopped engine you can't get going again. If it must be done, it should be at altitude, and with a briefing. The affect is the same far form the ground, and close to it. I am required to stop and feather engines on twins during flight testing sometimes, it gives me the willys, and I orbit high over the airport.
There's no real need for instructor drama during training. Accidents happen then too, and it's nice to be able to explain to the insurance company that you were doing everything to mitigate the chance of an accident. Deliberately stopping an engine would not be that!
There's no real need for instructor drama during training. Accidents happen then too, and it's nice to be able to explain to the insurance company that you were doing everything to mitigate the chance of an accident. Deliberately stopping an engine would not be that!
There are quite a few reports of people who practice forced landings regularly being caught out when they have to do one for real, and find that their glide angle is rather steeper than they expected when the engine is completely stopped, so I can see some rationale. I leave other people to decide how sensible the idea is - near a big runway I can see it might be arguable.
We call them 'glide approaches' as in 'downwind for glide approach' and not 'downwind for forced landing
'.
My favourite apocryphal story I've heard is of the student who has been doing lots of procedural training on the ground. When doing a pfl, and before the instructor can stop him, he deftly turns off the fuel, switches the switches, then pulls out the keys and throws them to the floor.
We call them 'glide approaches' as in 'downwind for glide approach' and not 'downwind for forced landing
'. My favourite apocryphal story I've heard is of the student who has been doing lots of procedural training on the ground. When doing a pfl, and before the instructor can stop him, he deftly turns off the fuel, switches the switches, then pulls out the keys and throws them to the floor.
Join Date: Jan 2012
Location: Ireland
Age: 40
Posts: 24
Likes: 0
Received 0 Likes
on
0 Posts
In the case of PFLs I find it good practice to turn off course 10° right/left when 'warming the engine' to allow for the extra lift generated. By the time you are back on track I like to think the effect is cancelled out. However, having been fortunate enough to not experience all going quiet Im not sure that this is of any real benefit... but I do like a challenge! 
Was the instructor sleeping at the time? 
I too know a similar chap!
4B
When doing a pfl, and before the instructor can stop him, he deftly turns off the fuel, switches the switches, then pulls out the keys and throws them to the floor.
p.s. I knew 'of' an instructor who would position the aircraft on a high final, give control to the student, pull the mixture then turn the ignition off and throw the keys over his shoulder into the back. Now THAT is daft!!
4B
My own opinion is that the risk outweighs the benefit of actually stopping the engine of a single at any point.
Why is there a better chance of the engine producing power again after the throttle is pulled and restored than after the mixture is pulled and restored? One line of thought says that induction icing is far more likely if you use the throttle to simulate zero thrust than the mixture.
Join Date: Dec 2011
Posts: 2,460
Likes: 0
Received 0 Likes
on
0 Posts
I would think that ICO would deplete the fuel piping of fuel, so it would take longer to get the engine delivering power, than if one closed the throttle.
That is why one does ICO to shut down: to make sure there is supposedly no fuel left anywhere near the engine (but you obviously know that).
That is why one does ICO to shut down: to make sure there is supposedly no fuel left anywhere near the engine (but you obviously know that).
Join Date: Sep 2003
Location: UK,Twighlight Zone
Posts: 0
Likes: 0
Received 0 Likes
on
0 Posts
I seem to recall that one of the certification requirements for a CofA aircraft is that it must restart following the mixture being pulled in flight?
Not that I would condone such an action which frankly is stupid. Why increase the risk when simulating it serves the same purpose?
Not that I would condone such an action which frankly is stupid. Why increase the risk when simulating it serves the same purpose?
Last edited by S-Works; 12th Jan 2012 at 11:17.
Join Date: Dec 2011
Posts: 2,460
Likes: 0
Received 0 Likes
on
0 Posts
Yes but the required maximum restart times require balls of steel if you are actually going to do it.
Cue the other debate about running one tank to empty, to be sure all one's fuel (well, for 99% of people, all the fuel they think they still have, plus or minus about 20%
) is in one tank and thus all usable.... I never agreed with that either, especially when flying in the very places where you might actually need to do that.
Cue the other debate about running one tank to empty, to be sure all one's fuel (well, for 99% of people, all the fuel they think they still have, plus or minus about 20%
) is in one tank and thus all usable.... I never agreed with that either, especially when flying in the very places where you might actually need to do that.
Join Date: May 2006
Location: Londonish
Posts: 779
Likes: 0
Received 0 Likes
on
0 Posts
I'm inclined to suggest that perception of risk is rather a personal thing. Why do we do anything, when often doing nothing is less risky - be that flying, rock climbing, crossing the road... or changing fuel tanks in flight? Presumably because we think the value outweighs the (additional) risk.
Assume it won't restart. *Personally* I'm of the opinion that a permanent loss of power *over a decent airfield* ought to be a complete non-event - which was why I wanted to clarify we weren't talking about a simulated off field landing. Frankly, I'm probably more worried that the fuel selector will fall off in my hand changing tanks at an inopportune moment. I'm also very glad I've experienced a true power out approach and landing, (right down to the roll out) - I found it a markedly different experience to a 'simulated' one, though I suspect that might be 90% psychological. I was surprised how much time I had to fluff around early on at height, and how quickly it all came up after turning final.
I wouldn't make it standard procedure, but for me there was definitely a value. Not sure it would have been as worthwhile if we'd re-lit and gone around.
Assume it won't restart. *Personally* I'm of the opinion that a permanent loss of power *over a decent airfield* ought to be a complete non-event - which was why I wanted to clarify we weren't talking about a simulated off field landing. Frankly, I'm probably more worried that the fuel selector will fall off in my hand changing tanks at an inopportune moment. I'm also very glad I've experienced a true power out approach and landing, (right down to the roll out) - I found it a markedly different experience to a 'simulated' one, though I suspect that might be 90% psychological. I was surprised how much time I had to fluff around early on at height, and how quickly it all came up after turning final.
I wouldn't make it standard procedure, but for me there was definitely a value. Not sure it would have been as worthwhile if we'd re-lit and gone around.
Thread Starter
Join Date: Dec 2010
Location: France
Posts: 50
Likes: 0
Received 0 Likes
on
0 Posts
Thanks all for your thoughts and detailed replies: interestingly, it looks as though posters are divided on this one?
As Genghis said, there are a lot of "it depends". To clarify, I was getting re-checked out on a 120 hp Robin DR400, we were the only ones in the circuit at the time, the wind was about 15kts on the ground, maybe 20kts+ in the air, no crosswind to speak of, paved runway is 1100 m x 20 m with a shorter but wider grass strip adjacent to that, separated by a shallow ditch. We took the paved runway.
There was definitely no expectation I would attempt to restart the engine and the controls were firmly with me. This was a power-out approach and landing through to roll-out.
Well, I just wanted to see what other folk think about this, and get a feel for whether it's common practice. Seems like it's an exercise that's not done frequently, but done all the same.
Mad Jock: yes, I was wondering about engine considerations. What are gingers, btw?
Mark1234: I can see how useful glider experience would be, it's on my "to do" list
As Genghis said, there are a lot of "it depends". To clarify, I was getting re-checked out on a 120 hp Robin DR400, we were the only ones in the circuit at the time, the wind was about 15kts on the ground, maybe 20kts+ in the air, no crosswind to speak of, paved runway is 1100 m x 20 m with a shorter but wider grass strip adjacent to that, separated by a shallow ditch. We took the paved runway.
There was definitely no expectation I would attempt to restart the engine and the controls were firmly with me. This was a power-out approach and landing through to roll-out.
Well, I just wanted to see what other folk think about this, and get a feel for whether it's common practice. Seems like it's an exercise that's not done frequently, but done all the same.
Mad Jock: yes, I was wondering about engine considerations. What are gingers, btw?
Mark1234: I can see how useful glider experience would be, it's on my "to do" list
Last edited by FlyingLapinou; 12th Jan 2012 at 14:01.
As described, whilst it's not an exercise I'd make a habit of, it's not a bad one and from 2000ft I think acceptable.
I would however probably (if an instructor did this to me) in the first instance on my touch drills say "oh gosh, the mixture has been accidentally set to ICO, I'll increase it to rich and see if the engine will restart")
G
I would however probably (if an instructor did this to me) in the first instance on my touch drills say "oh gosh, the mixture has been accidentally set to ICO, I'll increase it to rich and see if the engine will restart")
G
I would think that ICO would deplete the fuel piping of fuel, so it would take longer to get the engine delivering power, than if one closed the throttle.
interestingly, it looks as though posters are divided on this one?
MEP debate and another.
Schiff's view
FAA advice
SEP Accident and MEP accident
Join Date: Feb 2011
Location: Hove
Posts: 72
Likes: 0
Received 0 Likes
on
0 Posts
The problem with those examples, Bookworm, is that none of them pertain to FL's situation, ie a glide approach to a full stop landing.
Questions as to whether the engine will restart before touchdown, or whether the student will shut down the other engine are irrelevant when the intention is to land a SE aircraft with the engine shut down.
I would argue that an experienced instructor in a simple aircraft should be able to perform an engine off landing onto a reasonably sized airfield with a 100% success rate. Students who have been taught to do the same will be a lot more confident & capable of coping with a real engine failure.
I learnt at a reasonably busy airfield, all my 'glide' approaches were with the engine running. It would have been nice to do a few engine off glide approaches.
Questions as to whether the engine will restart before touchdown, or whether the student will shut down the other engine are irrelevant when the intention is to land a SE aircraft with the engine shut down.
I would argue that an experienced instructor in a simple aircraft should be able to perform an engine off landing onto a reasonably sized airfield with a 100% success rate. Students who have been taught to do the same will be a lot more confident & capable of coping with a real engine failure.
I learnt at a reasonably busy airfield, all my 'glide' approaches were with the engine running. It would have been nice to do a few engine off glide approaches.
Join Date: Dec 2011
Posts: 2,460
Likes: 0
Received 0 Likes
on
0 Posts
The problem is there is no such thing as a 100% success rate in this game.
Not when landing on a normal GA sized runway.
The student might do something daft like drop the gear or the flaps, and then where has your glide ratio gone?
One should simply not take risks like this. It is pointless. In the extremely rare chance of a real engine failure, most pilots who can fly can put it down into some field - IF there is a field.
Not when landing on a normal GA sized runway.
The student might do something daft like drop the gear or the flaps, and then where has your glide ratio gone?
One should simply not take risks like this. It is pointless. In the extremely rare chance of a real engine failure, most pilots who can fly can put it down into some field - IF there is a field.
Join Date: Feb 2007
Location: Amsterdam
Posts: 4,598
Likes: 0
Received 0 Likes
on
0 Posts
I don't agree.
IF the student has shown to be able to do multiple PFLs with good success (like normal, with the throttle closed/mixture rich) and IF you have a nice wide, long and quiet runway available, I can certainly imagine that the instructor would pull the mixture to ICO and let the student perform a proper glide landing. For instance as the capstone landing after a training session on PFLs.
Provided that the instructor watches the student like a hawk and doesn't let something silly happen, like dropping full flaps too early, this can be done safely, IMHO.
And it's a great confidence booster. We all know that with the throttle closed the engine still delivers a bit of power, and if things go bad, you can always go around. But to pull off a successful PFL with the mixture closed, you really have only one shot. Plus, the flight characteristics of the aircraft are for real - there is no idle thrust. In a sense it can have the same confidence booster value as sending someone first solo.
And hey, gliders do this all the time, safely. You just have to know proper heights, glide angles and so forth.
But I agree that PFL training by default should be done with the throttle closed. Using the mixture to stop the engine should be an exception, and only under the conditions described above.
IF the student has shown to be able to do multiple PFLs with good success (like normal, with the throttle closed/mixture rich) and IF you have a nice wide, long and quiet runway available, I can certainly imagine that the instructor would pull the mixture to ICO and let the student perform a proper glide landing. For instance as the capstone landing after a training session on PFLs.
Provided that the instructor watches the student like a hawk and doesn't let something silly happen, like dropping full flaps too early, this can be done safely, IMHO.
And it's a great confidence booster. We all know that with the throttle closed the engine still delivers a bit of power, and if things go bad, you can always go around. But to pull off a successful PFL with the mixture closed, you really have only one shot. Plus, the flight characteristics of the aircraft are for real - there is no idle thrust. In a sense it can have the same confidence booster value as sending someone first solo.
And hey, gliders do this all the time, safely. You just have to know proper heights, glide angles and so forth.
But I agree that PFL training by default should be done with the throttle closed. Using the mixture to stop the engine should be an exception, and only under the conditions described above.
Moderator
I'm not so concerned that the engine would restart - it will.... unless the not so robust mixture control cable breaks when someone pulls too hard on it, then you're not going to get it to rich again. This has happened - is it worth the risk? Not for me.....
I don't agree.
IF the student has shown to be able to do multiple PFLs with good success (like normal, with the throttle closed/mixture rich) and IF you have a nice wide, long and quiet runway available, I can certainly imagine that the instructor would pull the mixture to ICO and let the student perform a proper glide landing. For instance as the capstone landing after a training session on PFLs.
IF the student has shown to be able to do multiple PFLs with good success (like normal, with the throttle closed/mixture rich) and IF you have a nice wide, long and quiet runway available, I can certainly imagine that the instructor would pull the mixture to ICO and let the student perform a proper glide landing. For instance as the capstone landing after a training session on PFLs.
Also for every total engine failure accident statistics suggest there are 2 partial engine failures, another scenario which is often totally ignored in PPL training and where PFL's with the engine actually shut down do nothing to prepare the students
The reality is that the least likely scenario for an actual real world engine failure is when a aircraft with sufficient uncontaminated and properly selected fuel, no carb ice and which had a normal runup and developed full power on takeoff; suddenly has the engine completely stop with no warning.......yet this is the exact scenario that is exclusively taught in flight training to prepare students for an "engine failure".
Join Date: Feb 2007
Location: Amsterdam
Posts: 4,598
Likes: 0
Received 0 Likes
on
0 Posts
True. Not to mention the subtle clues that engines may give you before they fail altogether. Who was ever taught to do an airborne magneto check? What if the oil temperature rises without explanation? Has anyone ever run a tank dry during training, simply to see what happens and how long it takes for the fuel lines to fill themselves from the other tank after selecting it?
