Selecting flaps during turns

[Double Back]

It was a loooong time ago during my ab initio training that we were instructed not to increase a flapsetting during turns, as the plane could stall because of this. (old Saab Safir with good a old biceps powered flap lever.) The argument was it could stall because of this, and because we all were Young lads we never questioned it.
Remarkably (it was around 1975) nearly all of the then group of instructors were ex-mil jocks.
Later I completely forgot about this, it never came back during training in any of my +/- 100 types I have flown.
Till last week when i needed a checkout on a C172 because of a medical stop of one Year and I was checked by an ex mil pilot who remarked my occasional flap setting change during turns. (with normal circuit speeds...)

I answered a bit laughing that was old and obsolete theory, but I did not convince him.

Anyone recognize this and give me some powder I can shoot back? :).
(btw I am at an extremely well relation with this chap, no worries!) :)

Richard

[Greek God]

I have never heard of increasing flap during a turn decreasing the stall margin. Load factor possibly but stall??
Conversely, I have always been cautious of raising or decreasing flap in a turn and even now I dont like doing it without a healthy margin. These youngsters doing an SID with a close in turn requesting flap retraction 2 nanoseconds after Fr next.

[pulse1]

I too seem to have picked up this concept somewhere in the past. My poor memory suggests that it was more due to the possibility of getting uneven flap deployment which would be more difficult to diagnose in a turn. Whatever the real reason, if there ever was one, it is still something I am conscious of while in the circuit.

[suninmyeyes]

I was taught this during a UK PPL in the 1970's. Like the post above it was explained to me it was in case of uneven flap deployment causing a roll. When I instructed in the USA and enquired as to whether they had a similar policy I was told it was a quirk of the UK and that Piper and Cessna had no such opinion on the matter. Since then I have had no qualms on extending flaps in turns in GA aircraft.

[B-757]

It was a loooong time ago during my ab initio training that we were instructed not to increase a flapsetting during turns, as the plane could stall because of this. (old Saab Safir with good a old biceps powered flap lever.) The argument was it could stall because of this, and because we all were Young lads we never questioned it.
Remarkably (it was around 1975) nearly all of the then group of instructors were ex-mil jocks.
Later I completely forgot about this, it never came back during training in any of my +/- 100 types I have flown.
Till last week when i needed a checkout on a C172 because of a medical stop of one Year and I was checked by an ex mil pilot who remarked my occasional flap setting change during turns. (with normal circuit speeds...)

I answered a bit laughing that was old and obsolete theory, but I did not convince him.

Anyone recognize this and give me some powder I can shoot back? :).
(btw I am at an extremely well relation with this chap, no worries!) :)

Richard

..All aircraft limitations can be found in the manuals..There is no such limitation in a C-172..
..This is a personal preference by your instructor..It may be a good technique (on some aircraft), but not a required procedure..

Fly safe,
B757

[CaptainProp]

It’s not a limitation, it is taught, as already mentioned, more as a technique to avoid additional control problems in case of split flaps.

CP

[Double Back]

Just to add, my experience includes 17 Yrs as commander on the B747-400 and I cannot remember ever having had this taught within our company. Yes there are procedures for asymmetrical flap movement but normally that happens at safe speeds within the retraction/extension speed range and they do not include a roll back to wings level item.
I only can recall one incident in a C172 with one of my fellow instructors in which the mechanism failed partially and it extended only one side. There is time and controllability enough to counteract the rolling moment with ailerons. He selected the single one back and made a flapless landing. A no brainer.

On the contrary, in Cessna aircraft I love to leave a (trimmed) downwind altitude with a 10 flap configuration by reducing power, rolling in for base and adding flaps in the turn. The power reduction and the increasing bank drop the nose (which is safe), and the flap increase somewhat recovers this downward nose movement, just a little nose Up trim needed an it stabilises on the base leg speed.
But that technique will not fit all a/c, likely a low winger will do different.

[vapilot2004]

Stall speed: flap deployment generally increases the stall margin - turning, decreases it. Stall concerns would seem to be an unlikely training point, unless flap retraction was the concern. Meanwhile, flap asymmetry recognition is certainly reasonable in training.

The most obvious reason, perhaps: Deploying the flaps adds an extra layer to pitch trim for students. For most aircraft in standard approach configurations, the two actions cause changes in wing load and configuration where pitch requirements are opposite upon turn entry, and additive at rollout.

[parabellum]

Not so much on light aircraft but from the BAC1-11 upwards I remember changing flap in a turn was not approved, (company), in case there was asymmetric movement of LE or trailing edge flaps. Don't recall stall speed being mentioned.

[Mach E Avelli]

The mantra of not selecting flap in a turn most likely stemmed from WWII experience. Aircraft returning with damage sustained in battle did not need to pull any more surprises on their overwrought crews with asymmetric flap while turning.
However, almost every transport aircraft certified in the last 50 years has has asymmetry protection designed into the flap system. Light piston aircraft are not required to have such protection, though several light turboprops have it.
I have yet to read in official manufacturer documentation any prohibition on selecting flap in a turn on any civilian aircraft, be it Cessna or Boeing.
So, it seems this one needs to go to the OWT basket.

[icemanalgeria]

I remember having the same thought when I started to fly Big jets (767). it didn't feel like good airmanship to select flap in the turn, I'd flown Golden Eagles etc before and my thoughts on those light twins were about getting flap asymmetry and late recognition.

[Fursty Ferret]

Flaps decrease the margin to the stall compared to the clean wing at the same AoA, so it’s plausible advice (if a bit paranoid). It's possible that they're thinking about an accelerated stall in a level turn, or of the lower wing stalling during a descending turn and leading to loss of control.

I think you'd need to be on the very limit of aircraft performance to even be close to those scenarios; a 30° turn only increases stalling speed by 7%.

In a transport category aircraft I wouldn't be concerned. There's a reason the slats sequence first during flap/slat extension.

[Vessbot]

The right set of circumstances could come together as the flaps are deployed

1. in the middle of the turn, G is increased to tighten it up for unforeseen (but foreseeable) circumstances
2. extra drag from the G slows the plane
3. extra drag from the flaps slows the plane
4. pitching moment from the flaps slows the plane
5. crew is too distracted by #1 to act on the speed decay vis-a-vis power or trim, and too task saturated from everything. They only pull back more on the yoke to counteract the descending tendency, thus slowing the plane more

Planes have been stalled for stupider reasons than that, so I believe it.

[ZeBedie]

Not so much on light aircraft but from the BAC1-11 upwards I remember changing flap in a turn was not approved, (company), in case there was asymmetric movement of LE or trailing edge flaps. Don't recall stall speed being mentioned.

The 1-11 didn't have any leading edge devices.

[Mach E Avelli]

My recollection of the BAC 1-11 was no L.E. slats, but I think it did have flap asymmetry cut out. Big flaps had quite an effect on stall speed - all favourable - so I still can’t see why an operator would prohibit selecting them in a turn unless they expected to take a missile strike at some time.
Years ago I experienced flap asymmetry in a DC3. As full flap was selected there was a nasty cracking noise and the old beast rolled very rapidly. Although it was controllable, we guessed one side had fully retracted, while the other side had fully extended. We took a punt and selected flaps up. This stopped the rolling tendency. DC 3 flaps don’t affect the stall speed by much, but they sure make great spoilers!
The problem was a hydraulic actuater rod had sheared its end fitting.

[JPAirbus]

Technically the flap deployment leads to an increased AoA (chord line "pitch up" while lowering trailing edge devices). At the same time flap deployment increases drag, which reduces TAS at a fixed power setting, which requires an even higher AoA to maintain the same lift.
Bank during a turn increases g-load demands and hence needs a higher AoA to produce the same lift at a given speed.
If you would have been riding at or near the max AoA prior initiating the turn you might get into trouble. If you are in a deceleration "flow" the adding of flaps might cancel out trim requirements during deceleration, hence leaving you with a "minimum effort manoeuver".
Split flaps are an additional problem. That´s harder to recognize and to handle in a turn (as compared to straight and level).

[suninmyeyes]

There's also a 50% chance that if flap comes out asymmetrically in a turn it will roll you towards wings level! This thread started out about advice given to pilots of light aircraft but has moved on to cover modern airliners which have built in flap asymmetry protection and where no advice about avoiding deploying flaps in a turn has ever existed. Oh the joy in a 747 of working out whether it was a split flap or assymetric flap condition. I remember in simulator details Captain, Copilot and Flight Engineer writing on a piece of paper which one they thought it was. Frequently two would think it split and one assymetric.

[RAT 5]

I hope no eager beaver CP's are reading this and think their SOP's need a revamp and tweaking update. There could be an endless list of things that people could dream up where they fall into the category of 'I wouldn't do that just incase something else goes wrong.'

I did come across a training captain from a neighbour airline whose personal opinion was to teach not setting the park brake when 'line up & wait' on the runway. Why? The brakes might stick on and you block the runway. Like I said the list could be endless if you let your imagination go wild.

[Vessbot]

Sounds like the Good Idea Fairy visited!

[vilas]

This practice was on archaic aircrafts like the DC3s may be some Russian aircraft like AN12(not sure). That too the concern was flap asymetry or runway on one side causing a rapid roll which may compromise aileron Control. But definitely not for stall considerstion. All today's aircraft have protections which make this concern superfluous and none of the airliner documents mention a word about it. Observing some obsolete caution because of habit is not the way to go.

[parabellum]

Thank you ZeBedie, I do remember the BAC1-11 didn't have LE devices but everything after that did so I included them as high lift devices that, if they ran asymmetrically, during a turn, could also spoil your day.:)

[Cornish Jack]

From memory - the American Airlines Upset Recovery video recounts the introduction of the 757 and a check on the inboard flap asymmetry case (in the Sim) with eye-watering results!

[sheppey]

I did come across a training captain from a neighbour airline whose personal opinion was to teach not setting the park brake when 'line up & wait' on the runway. Why? The brakes might stick on and you block the runway. Like I said the list could be endless if you let your imagination go wild.
Interestingly I was informed just the other day by a former military pilot that not setting the park brake at the holding point or when lined up on the runway was SOP at RAAF Central Flying School a few years ago. . The reason given was a single instance where a pilot overseas was lined up with park brake on awaiting take off clearance when he realised another aircraft was on very short final and intent on landing. The pilot on the runway gunned the throttle to clear the runway but in his haste forgot the park brake was on. The crash was inevitable. A statistically improbable event and certainly no reason to not have the park brake on whenever an aircraft is stationary anywhere.

[Clare Prop]

To be certified under Part 23 the aircraft must still be controllable following failure of one primary control system. eg be able to control roll with rudder if ailerons fail, attitude with trim if elevator fails etc.

In testing a type that I fly, they had to test fly with one flap at zero and one at 30% and still be able to control roll with aileron, which the aeroplane easily did or it wouldn't have been certified.

So I call bull**** on the "never put flap down in a turn" theory, unless it is in the limitations section of the POH and I've never seen it there in any of the types I fly.

[stilton]

Years ago I flew with a chap who wouldn’t
use more than 20 degrees of bank (B727)
in any mode of flight


I asked him why and he informed me when you did this the aircraft would ‘disappear on radar’


He was stealthy ahead of his time..

[spleener]

Interestingly I was informed just the other day by a former military pilot that not setting the park brake at the holding point or when lined up on the runway was SOP at RAAF Central Flying School a few years ago. . The reason given was a single instance where a pilot overseas was lined up with park brake on awaiting take off clearance when he realised another aircraft was on very short final and intent on landing. The pilot on the runway gunned the throttle to clear the runway but in his haste forgot the park brake was on. The crash was inevitable. A statistically improbable event and certainly no reason to not have the park brake on whenever an aircraft is stationary anywhere.
From memory, that procedure was to align with formation takeoff procedures.....Giving/receiving the nod to roll with the parkbrake on ....

[meleagertoo]

I've certainly not come across this in 30 years of Mil and Civ flying but think the inability to change flap settings in a turn (ie change speed in a turn) would severely limit one's ability to operate freely and flexibly in a busy air traffic environment.
Almost all modern transport aircraft have some form of asymmetric flap protection which would render this technique rather pointless anyway.

[Atlas Shrugged]

Why is there a constant need to over complicate everything?

A turn has no bearing on flap extension or retraction.

Speed and the relationship to angle of attack and minimum speeds, of course, is very relevant. If you are too slow to retract flaps in the turn, then you are too slow. Period. Either speed up or wait. If you have adequate energy, margin, and speed, extend or retract in the turn.

Flap assymetry is flap assymetry, whether in the turn or not.

The aircraft doesn't know if it's in a turn or how high it is; flaps extended or retracted in a turn or 3 feet above the ground ..... it doesn't know or care where or when. It can't think, it can't see and last it knew, it was perfectly happy and content two seconds before you flew it into the side of a mountain.

Raising or extending flaps is perfectly safe in a turn, if you do it properly. Raising the flaps at 5 feet above the ground is perfectly safe, if done properly.

It should be done sensibly, just like anything else in an aircraft.

Your welcome...

[vilas]

Flap assymetry is flap assymetry, whether in the turn or not No! It is not. Without flap asymetry protection, in a turn it can cause substantial roll. But with the present aircraft with asymetry, runway protection you can retract or extend in a turn.

[Basil]

In the 1970s we were not permitted to alter flap settings in the Viscount whilst turning. We were told that the aeroplane had previous form with assym flap.
I remember that very well because, flying a tight arrival the voice from the LHS announced "I hope you aren't planning to extend flap in the turn, Basil, because you know it isn't allowed!" Bas had forgotten that The Boss was commanding that sector. :O

[Basil]

. . . .
I asked him why and he informed me when you did this the aircraft would ‘disappear on radar’ . . .

I wonder if he was confusing a/c bank with loss of contact for about one sweep in MTI.
Moving Target Indicator looks at the radial speed of the target and, if it is zero, assumes that it is a ground return and does not paint so, at the precise moment a passing target is tangential to the radar head, it will not paint on the PPI screen.
I guess, if you flew a perfect circle around the radar aerial, you wouldn't paint.

[Check Airman]

Asymmetry protection or not, if you're worried about that every time you're in a turn, you may be overthinking it a bit.

[Atlas Shrugged]

My point exactly!

[CHfour]

I hope no eager beaver CP's are reading this and think their SOP's need a revamp and tweaking update. There could be an endless list of things that people could dream up where they fall into the category of 'I wouldn't do that just incase something else goes wrong.'

I did come across a training captain from a neighbour airline whose personal opinion was to teach not setting the park brake when 'line up & wait' on the runway. Why? The brakes might stick on and you block the runway. Like I said the list could be endless if you let your imagination go wild.
I never set the parking brake on the runway if on a line up and wait but it's not about blocking the runway. If one of your brake packs fails to release (unlikely, I know) it would not be detected until the tyres burst. There was once a case where a take off was commenced on a partly contaminated runway with the parking brake set and the aircraft accelerated normally as the wheels slid on the contaminant. As the aircraft progressed onto an area of good BA, the tyres on the main gears blew. To be fair the config warning should have saved that one.

[vilas]

if you're worried about that every time you're in a turn, you may be overthinking it a bit. There is no thinking, the older aircraft of certain make you just didn't extend or retract in a turn. The present aircraft you extend or retract whenever you want to, appropriate speed is the only criterion.

[underfire]

Looking at the myriad of posts providing reasons for not applying flaps in a turn. To put this in perspective, all of these reasons such as stall, asymmetric operation, etc, would not all of those conditions be an issue at any point below 500 feet? (forget about turns)

Part 23 -- Airworthiness Standards: Normal, Utility, Acrobatic, and Commuter Category Airplanes
Mechanical interconnection requirement of Sec. 23.701(a)(1). This requirement is to ensure against hazardous asymmetrical operation of the flaps after any probable single or probable combination of failures of the flap actuating system. A probable combination of failures should be considered when the first failure would not be detected during normal operation of the system, including periodic checks, or when the first failure would inevitably lead to other failures. (Systems where a probable combination of failures may occur could include the electrical and hydraulic systems.) The airplane must also be shown to be capable of continued safe flight and landing without requiring exceptional pilot skill or strength following these failures. To demonstrate that the airplane is safe under these conditions, tests should be conducted with the flaps being retracted on one side and extended on the other during takeoffs, approaches, and landing. If there is a probable hazardous condition, a separate positive connection that is not part of the flap actuation system is required.

[Atlas Shrugged]

The airplane must also be shown to be capable of continued safe flight and landing without requiring exceptional pilot skill

Sounds like Squarebus Airbus......;)

[krismiler]

FAA DOT regulations: "Be able to maintain any required flight condition and make a smooth transition from any flight condition to any other flight condition without exceptional piloting skill, alertness, or strength, and without danger of exceeding the limit load factor under any operating condition probable for the type."

The A320 has automatic brakes which will immediately lock the flaps in the event of asymmetric deployment.

[Atlas Shrugged]

Yes, and if it trips, it will remove power to the devices, stopping them (only the symmetric panels) wherever they happen to be. Whilst it is a great idea, it puts another failure level into the system, as a problem with the symmetry protection can itself stop parts of the system from operating....so the flaps themselves might be fine, but the protections system isn't. That's a pretty benign failure though and a rare one.

The reality is that modern jets are every bit as easy to crash as were the older ones.

[jimtx]

I was in the back seat of an L1011 simulator when the sim pilot failed the asymmetry protection in flight on final. I glimpsed a blink on the annunciator panel but before I could focus on that we were rolling after the captain called for the next notch of flaps. Full opposite wheel did not help as we crashed and burned. My takes: the most important pre flight check on that bird was the annunciator panel light check, if something crazy happens undo the last thing you were doing. If the sim aero was correct full wheel could not correct the asymmetry. Maybe additional rudder would have. This is only in regard to aircraft asymmetry certification requirements. I will change flap settings in a turn.

[Atlas Shrugged]

Here's something albeit in a slightly different direction. Not me, but it did happen. Your destination is Wellington NZ, light rain, nil wind. Aircraft 767. Final approach. Upon selecting landing flap, flap asymmetry warning, flaps frozen. Cannot be moved at all. Dirty go around. Checklist action gives approach speed Vref 20 + 20, about 165 knots. Runway length required is well beyond the length of the runway. Even with alternate fuel, diversion not possible as alternate fuel never assumes that the aircraft will be dirty (and limited to FL200). What could be done?

[oggers]

What could be done?

Ooh interesting. Firstly you would dump the useless fuel. That would reduce the Vref and LDR. Then you could even slow to below the new Vref knowing that the stall would theoretically occur a shade under 75% of Vref. If you used 90% of Vref you would still have a comfortable margin and your landing distance would be reduced approximately 20%.

[Vessbot]

Is that runway required with or without the 60% factor?

[Mach E Avelli]

Advise emergency services of potential brake fire.
Burn or dump fuel down to minimum reserve plus enough for a second go just in case first go is untidy.
Complete appropriate checklist and fly appropriate speed for weight. Going below Vref for config invites a tail strike, so don’t do that!
Fly stable approach to touch down, do not accept float, a firm landing on the spot is what you want.
Land and throw everything at stopping - spoilers, brakes, reverse.
Exit runway if possible, but do not taxi to the ramp.
Complete hot brakes checklist.
Think aloud throughout - for the benefit of the tape.
Complete paperwork as to why you did not have the full performance ‘buffers’.
Tech Log entry to change brakes, wheels, tyres or whatever MOM calls for. Maintenance will want touch down groundspeed and rate of descent, so it is helpful if the FO can make a mental note of these. If not, give them PIDOOMA. or they can probably access it via QAR.

Been there and done it twice; both occasions the runway was limiting. One tyre fuse plug blew on one occasion, but only after we stopped.

[Journey Man]

Is that runway required with or without the 60% factor?

The proposed situation occurs once airborne. Dispatch planning no longer relevant.

[Vessbot]

The proposed situation occurs once airborne. Dispatch planning no longer relevant.

No matter, the "Runway length required" that Atlas Shrugged got and that was "well beyond the length of the runway" either does or doesn't include the extra pad, and its inclusion vs. exclusion drastically changes the picture.

[Mach E Avelli]

If you don’t have enough fuel to divert, nothing changes, except perhaps whether you call it a Mayday and put the pax in the brace position. I would only be going to that extreme if the runway was so short that an over run was likely. In the case of Wellington and a B767 I rather doubt that.
But if an over run WAS clearly inevitable AND a longer alternate could be safely reached by ignoring the FL200 limitation, I would rather go to the alternate.
The FL200 limitation does not mean that the aircraft will crash if it is exceeded.

[EIFFS]

Boeing NSB 12 bulletin ( Boeing 737)

2. Maneuvering during flap​ retraction from Flaps 1​ to​ Flaps Up after takeoff ​
or during a missed approach when Engine Anti-Ice is ON or when Wing​ ​
Anti-Ice has been selected ON after liftoff.

NSB 12 describes nuisance stall warning stick shaker events that can occur under certain circumstances including item 2 described above, the mitigation is to reduce bank angle to 15 degrees.

[B2N2]

The right set of circumstances could come together as the flaps are deployed

1. in the middle of the turn, G is increased to tighten it up for unforeseen (but foreseeable) circumstances
2. extra drag from the G slows the plane
3. extra drag from the flaps slows the plane
4. pitching moment from the flaps slows the plane
5. crew is too distracted by #1 to act on the speed decay vis-a-vis power or trim, and too task saturated from everything. They only pull back more on the yoke to counteract the descending tendency, thus slowing the plane more

Planes have been stalled for stupider reasons than that, so I believe it.

This ^^^
You can’t compare a multi engine jet with a light SE.
In a light GA aircraft you simply don’t have the excess power or performance.
Inexperienced pilots or pilots with very marginal currency should avoid flap extension or retraction in a turn. Climbing or descending.
I always instructed my students not to do it.
During a turn you should be concentrating on other things and aerodynamic changes are a distraction.

[theNotoriousPIC]

If you don’t have enough fuel to divert, nothing changes, except perhaps whether you call it a Mayday and put the pax in the brace position. I would only be going to that extreme if the runway was so short that an over run was likely. In the case of Wellington and a B767 I rather doubt that.
But if an over run WAS clearly inevitable AND a longer alternate could be safely reached by ignoring the FL200 limitation, I would rather go to the alternate.
The FL200 limitation does not mean that the aircraft will crash if it is exceeded.






You might be right, but might be wrong. For my aircraft Embraer decided that flying above FL200 with flap out was too dangerous because of critical mach and buffet problems. They state multiple times in the AOM (and my airline repeats in SOP) that this limitation is not to be exceeded. The QRH says in all instances that if we have a flap retraction issue that FL200 is our top altitude.

[Check Airman]

You might be right, but might be wrong. For my aircraft Embraer decided that flying above FL200 with flap out was too dangerous because of critical mach and buffet problems. They state multiple times in the AOM (and my airline repeats in SOP) that this limitation is not to be exceeded. The QRH says in all instances that if we have a flap retraction issue that FL200 is our top altitude.

Your embraer won't crash. Don't ask how I know.

[hans brinker]

Fixed it for you:


Your embraer won't crash. Don't ask how I know.

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What you meant to say was "mine didn't crash"

[Mach E Avelli]

The original reasoning behind the 20000 ft limitation for flap extension (for Boeing at least) was that there was such a small probability that flaps would ever be required above that level, there was no point in extending the test program to validate handling. Perhaps Embraer thought the same. Certainly, had their aircraft exhibited any undesirable handling at FL200 during the test program, they would have either addressed it, or imposed a lower flap extension limit to provide a safety buffer.
Built-in asymmetry protection is expected to safeguard handling if the flap system goes out to lunch, but can't be expected to cover cases of other structural failure. One such case occurred with an old B732 which had the L.E. slat on one side partially break loose and wrap itself back over the wing during a missed approach. The crew found themselves in the classic 'between a brick and a hard place' situation. They could not land at the destination because the weather and runway length etc made that far too risky. But as they climbed out to divert to the alternate the aircraft quickly reached a speed where roll control was no longer possible. Fortunately, by very careful handling of speed, altitude and thrust they did make it to the alternate, but ate into their final fixed fuel reserve to do so.
A crew fixated on observing all limitations may well have decided to ditch. In the dark, over open sea, that would have been a far worse outcome.

[Check Airman]

Fixed it for you:




What you meant to say was "mine didn't crash"
That assumes that I was there at the time, which I will neither confirm nor deny.

I'll definitely use that disclaimer in the future though :)

[hans brinker]

That assumes that I was there at the time, which I will neither confirm nor deny.

I'll definitely use that disclaimer in the future though :)

:)

fillerfiller

[t-bag]

Are any commercial airplanes certified for flaps above FL200 ( note - certified)?