Flap retraction
 

Ok.. I'm bored of the ryanair private jet thread so can anyone put me straight on this..

On a normal all engines operating take off in a business jet we get airborne, romp through V2, go through the speed that the manual says the flaps can go up (V2+20 in mine) and then the most common trigger in companies I have worked for use a height trigger (400 feet for some, 1500 in the one I've just left) to retract the flaps. The challenger is regularly doing 200 ish by that point which is V2+70. I have tried to have the argument many many times that the wing doesnt care how high up it is and we should simply manage the drag the way the manufacturer intended but nobody is having any of it.

What do other people do?

Think the point is nothing to do with the wing. Its about the chance of moving the wrong switch close to the ground and giving yourself a bit of height to get out of trouble if needed.

really? Whats your go-around height on an ILS then?

Company SOP 1000ft (agl), both donks or OEI.

I agree with you though, oei or on a noise departure, you manage the speed, but on a normal day, best to manage the drag.

if you are going so fast close to the ground, why not pull the nose up a bit and gain more altitude?

you may be super light on a reposition flight...do you have option of reduce thrust takeoff?

except for two special airports, we start clean up at 1000' agl, and reduce power at 3000'agl/afe

Deck angle vs gin and tonic in the back!

Derate not allowed by company. Glex climbs like a homesick angel even at max tow.

Why do companies have all engine operating heights for retracting the flaps. In the case of your global for instance, what has height got to do with anything? I realise its an SOP (it is for most companies) but where does it come from? Its got nothing to do with the manufacturers. For the challenger the flaps can be retracted at V2+20. So why does anyone wait for a height?

At my company we call flap speed at V2+25 but do not make any turns until 400' agl.

TomM

It is a double edged sword! Extension of flaps on landing ie in the descent has the effect amongst other things of increasing drag and lift but the aircraft is descending so tapping into potential energy as another source of energy supplied by the engines.
The drag helps control the speed the lift allows the aircraft to fly at VREF for landing.
Takeoff is different we have the lift required to takeoff at a relatively slow speed but with that comes the drag.
Not just from the takeoff flap setting but from the gear and increased AOA!
The gear we get away quickly but we are at max N1 and at slow speed with no potential to tap into potential energy from the airframe should for any reason we need it and limited ability to reduce AOA.
Obviously the main concern in cleaning up in event of an engine failure or loss of power but there is another!
In still air all well and good but in shear conditions that slow speed can become critical.
Hence it is better to concentrate on flying the aircraft in a stable condition until well clear of the ground where you have the ability to tap into potential energy should you need to as well as reducing drag by reducing AOA before going from flap takeoff to zero.

Some say 400agl some 1000agl

Pace

Hello!

In my part of the world, most major airports have noise abatement rules that call for a V2+10kt climb until passing 1500ft AGL before retracting flaps and accellerating. Therefore, many operators have made this (totally arbitrary!) 1500-figure part of their SOPs. Luckily, we are still permitted to do what we want if we precede it with "non standard" ;)

max

About the same as yours, for Cat I...

What I'm trying to suggest is you separate the act of getting airborne with the act of retracting the flaps. Think of it this way, by the sounds of the performance of your jet, you could probably get airborne and by the time you are airborne and have selected gear up, you could probably select flap 0 too.

So, you spend a good few years safely doing this. But you are now at the end of a veeerrrrryyy long week, end of an even longer day and an engine has just failed on you. Unfortunately your motor skills training says that when you select gear up, the flaps go too....

Its about, as I suggested above, error management.

And I'm not suggesting that it would be YOU making these mistakes, just that its possible...

You obviously do not know him then.

Moutrie,
Its all to do with the profile, you raise the flaps at a height to take into account obstacles, NADP 1 NADP 2. If you are flying too fast for the flap speed then manage your speed...
If you retract too soon and then have an engine failure you might not clear the obstacle or on a two engine take off earn yourself a fine for noise...
The wonderful Capt Dyer knows that. He is a sky God...

now you see thats all very interesting info.
APANDY, I think your lot have got it spot on. Get rid of the drag as early as possible - ie, flap up as soon as you're V2+whatever the minimim is, and the no turns before 400' is straight out of document 8168 so that makes sense too.

But why anyone would link a flap retraction to a height is beyond me. I've heard countless arguments and I don't understand any of them! There are no circumstances that I'm aware of where the height makes any difference. A change in flap selection can only be made because of speed - it says so in every aircraft manual written, and it never even mentions height!

Where I think the confusion lies is that there are various certification platforms for an acceleration altitude (ICAO, for instance, use between 400' and 1500') for the acceleration platform in the event of an engine failure but this still is not the criteria for flap retraction - its only about speed!

The arguments about reaching for a lever in the dark on a windy night when you are a bit knackered and finding the wrong one are a bit bizarre to me. Its certainly not a reason to be climbing against the significantly increased drag of having the flaps down! Noise abatement is an interesting one - very few business jet operators I know fly proper noise abatement departures because of the problem of limiting body angle (actually I don't think this is the real reason they don't do it - I think the real reason is they can't be bothered to train properly for it and believe their aircraft are quiet enough thanks very much and they are probably right). But even that doesn't justify leaving the flaps down and increasing the speed against that drag.

What I'm really interested in is where on earth the idea came from that flap retraction is linked to height. In lots of companies its the first call that isnt speed related and I have seen loads of COR's and MOR's related to forgetting to retract the flaps because the 400' call was missed. Big problem here, height is the wrong call to trigger retracting flaps - should be the V2+ call, and its PM moving the eyes to a different instrument at a critical moment that may be at the heart of this. What also bothers me is that some people think that an engine failure means you do something different with the flaps than what you do if the aircraft is operating with all engines (which is at the heart of companies choosing an arbitrary height for both). You DO do the same thing in the event of an engine failure - retract the flaps on the correct speed schedule...

what do you think..?

.. thought of something else pace..

regardless of the conditions, in the event of an engine failure you would fly your plane at V2 flapped to acceleration altitude, take the flaps up at the appropriate speed, and climb away at V2+minimum, then go to an enroute climb speed at an appropriate time. wouldn't you?

So why is there a fear among pilots that selecting flap up at V2+20 will somehow make your aircraft unstable or prone to turbulance? Because its a very common misconception. The amount of lift you need from the wing is significantly reduced in the climb and you will be somewhere around 1.5 Vs so where does the feeling that the aeroplane needs 40 or 50 knots of extra speed from. All we are doing is degrading the 2nd segment climb and therefore wasting fuel and making noise.

just a thought..

Historically this comes from airport design criteria which were matched to aircraft design. Around a round table (many round tables over the years) starting in the 1930ies, representaives of towns and aerodromes and representatives of aircraft manufacturers debated over the obstacle-free zones around aerodromes and the climb performance of aircraft. The aerodrome managers wanted to build as close to town centres as possible, the aircraft manufacturers wanted to use the cheapest engines on the market, and eventually that 400ft compromise evolved that found it's way into both aerodrome layout and part-25-design criteria. If someone wants to do a historical search, I'm pretty sure that 400ft-obstacle which was the origin of all this can still be identified somewhere. Some building around Idlewild or Tempelhof, who knows...

But where on earth this 1500ft-figure came from is a miracle to me. Totally arbitrary, nonsensical, yet part of many training programs and SOPs. Personally, I tend to disregeard it with the exception of my yearly checkride at FSI.

You have to understand that while we scratch our heads at the rationale of some checklists and SOPS, the reality is that you had a bunch of pilots and lawyers in a room cooking this stuff up at certification time....

'Ok, imagine the lowest time, pal/buddy/robot, Chief pilot culled inexperienced moron flying this plane...next to him is a pilot with even less time, less balls..a marshmellow, hoping the pilot has it right, because he's not going to say anything...so when do we have this guy retract the flaps?'

'Well if we have him do it right way...some guy, some where is going to rotate right at stall, then retract the flaps...can't have that...if we make him wait until 1500 feet, chances are some moron will accelerate to 300 kts and rip them off....so tell you what...let's make it 400 feet.....high enough where idiot #1 won't do it to quick.....not so high that idiot #2 will accelerate past Vfe. All those in favor say aye. Now just to cover our butts, let's make the climb out speed less then Vfe, so figure the times to climb for that...ok...so what am I missing? Come on guys...try to imagine a complete retard flying the plane.....what have we missed...yeah yeah...that's right...get the AP on fast...no early turns....good good keep them coming...'

whats next
yes the 400' is part of document 8168 - its in the procedure design criteria bit in section 2 but it still has nothing to do with flap retraction.

Sillypeoples
you're kind of proving my point.. its got nothing to do with height. So when you say newbie might do it at this point or that point the only bit that matters is selecting them at the right speed. In fact, this is exactly where all the confusion comes from!

starting to see a theme here..

So, is there any reason at all for having a height trigger? Has anyone ever seen such a trigger in an aircraft manual?

I'll tell you where I think it all comes from. Flight flipping safety! I'm gonna ask them see if they know..

It's to do with the distance it takes to get from V2 to flap retract speed when an engine fails, each take off or intersection has in theory a different altitude to raise the flaps governed by what you may fly into on the take off flight path.

400 feet is the minimum by regulation, do you really want to fly level at 400 feet trying to speed up to flap retract when it's 40 degrees at Al Bateen and you are heading towards downtown Abu Dhabi at MTOM.

In the mountains you may need to fly V2 to your engines 5 or 10 minute limit before being able to fly level for flap retract. If you don't buy take off perf or calculate it like we are supposed to then 1500 feet has got to be safer than 400 feet for level acceleration?.

hello mr k

I can do a first principles net take off flight path calculation, thats not the issue here. My problem is that all engines operating, most biz jet pilots go rattling through the speed that they can retract the flaps and continue on up to whatever speed they get to by the time they get to 1000' or 1500' or whatever their particular company chooses to to use as a totally arbitrary flap retraction height.

Flap retraction heights don't exist - they are a figment of crappy understanding. There are level acceleration platforms which you can use to get from V2 to whatever speed you need to raise the flaps to the next position but all engines running you don't need them. So you can raise the flaps whenever you like as long as you have achieved the necessary speed.

Its incredible to me that very very few of us do whats in the aircraft manual. A mixture of tribal knowlege and lack of understanding has taught an enormous number of people to do something that doesnt make sense and can't be justified.