Accident Report F27 - SOP retract flaps right after T/D !

[Tartan Giant]

I was reading the accident report (www.open.gov.uk/aaib/gbncy.htm) about the F27 that slid off the R/W at Guernsey (Dec 1997) after a long landing in very testing conditions (x/w outside limits it transpired) and came across the operators SOP whereby the flaps are retracted very shortly after touch-down; intending to lessen the lift from the wings and put more weight on the wheels.

I am surprised that this a/c (or any) needs to retract flap, to reduce lift by some small margin, to gain some extra weight on the wheels, to assist in stopping the thing in the remaining LDA !

I have never heard of this method in a certification schedule for an aircraft to gain a C of A, or it being widely adopted by F27 operators.
Could somebody please explain the technical benefits of this F27 SOP and what proven extra weight is gained from lift reduction measures after landing, and the proven bettered LDR so achieved.

It seems a bloody stupid time to be retracting flaps to me - for any reason.
As always, I am willing to be enlightened.

[Professor Longhair]

Tartan Giant,

I flew as pax from Kai Tak to Kathmandu in a Royal Nepal 757 a few years ago ('93 I think, thought process: fly with the boys who know it the best!) and they dumped the flaps right after touchdown. Thought it might have some connection to altitude, but they did the same after landing at HKG as well.

Never encountered this anywhere else.

'Fess

[pegleg]

Tartan Giant.
I was taught to do this on my conversion to both the F27 and FH227 by Belgian and Finnish instructors respectively.As I recall it was recommended for wet/icy runways and although we certainly had wet in Africa the only ice around was in my brandy and coke!
I can't comment on the certification requirements and as by and large we landed on enormous runways can't say the benefit was noticeable. It was also SOP on the Citation I flew and it probably did help as we had no reversers. I never worried too much though as we had the Drag Chute fopr really scary moments!!
Cheers

[Buzzoff]

This was taught to Air Anglia/Air UK by the Fokker test pilots on day one. It's ten years since I flew an F27 but I seem to remember it being a condition of meeting the landing performance graphs.

[fireflybob]

You need to look in the Aeroplane Flight Manual (CAA, etc) to see what assumptions have been made to achieve the scheduled landing distance.
I know it's a light type but the same principal applies. If you look at the PA28-140 flight manual it specifies flap up after touchdown and max manual braking!

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[veewunrotate]

Pegleg, once you touchdown on a 757, the ground spoilers come up, dumping all the lift anyway, so lifting the flaps up during the landing roll is not only pretty pointless, I would go so far as saying it is dangerous in that it is taking the monitoring pilots attention away from the immediate task of monitoring the effeciveness of all retardation devices and the safe rollout of the aircraft.

[ozone ranger]

On the Sabre 40/60/80 series standard procedure is to raise the flaps after touch down so the full weight will be on the main gear. Don't know about any other aircraft that requires this however.

[Tartan Giant]

Thanks guys for taking the time and trouble on this one.

I do NOT have any experience on the F27 (all jet hours mostly).

I have to agree with "veeonerotate" on the B757 issue - raising flap after T/D is really a dangerous thing to do in this big A/C. It achieves nothing as explained.

I am still at a bit of a loss on the benefit of the procedure on the F27 though.
Having crossed the T/hold at Vat (and your added factoring) you basically "stall" the aircraft on touch down or very close to it (unless you were 'hot') then after landing the L/D ratio is in favour of the DRAG.

Is not the rudder big enough to cope with max ldg flap (40) in conditions of max demonstrated x/w ?
Or is there different x/w limits for different landing flap settings ?

Considering the F27 is a fairly large aircraft with a load of kinetic energy to kill after T/D, I would have thought (on limiting runways) in a x/w which was close to max permissible, keep the flaps down (or even put more down to increase drag after T/D) and full aileron and judicious use of rudder and NWS…..and of course selecting “ground fine”.

I know some will say, “you will weathercock with more flap”……this may or may not be a factor depending on what the CAA or other Authorities used as the schedule to demonstrate the minimum LDR with max flap and max x/w on this type.

As I recall, the F27 had a very ‘negative’ (nose down aspect) ground attitude, so I would have imagined there would not be much lift left after the nose-wheel was lowered in any landing situation.

Sorry to be going on about it, but I have yet to be convinced on this SOP !!

[zzz]

when I flew for Air UK this was the procedure we used in all conditions. When landing in max crosswind it was sometimes necessary to use rudder, nws and differential braking to keep straight on the rwy. I think the lack of directional control came from the single nosewheel which provided little grip, particularly in the wet. I think the procedure was used to get grip to the nose wheel asap.

cheers zzz

[pterodactyl]

Flew the F27 many years ago so can not remember the flap after landing bit but one thing I do remember is that most pilots failed to apply FULL aileron into wind as speed reduced. This was because they stopped when they encountered the back pressure of aileron spring tab operation. A considerable extra force was necessary and gave about 20 degrees extra control wheel input and had a most beneficial effect on control in a crosswind. The further down deflection of the downwind aileron and consequent drag had quite a substantial directional effect in a crosswind. Easy to demonstrate this extra control wheel available by operating the aileron control when parked.

[Tartan Giant]

Once again, thanks guys for giving me your thoughts, and in some cases your actual experiences with the F27.

As I admit to having no knowledge of F27 ops and having not seen any operational data which PROVES retracting the flaps after T/D reduces the landing roll, so I must close with the only “advice” I have seen via AIC’s on landing schedules for “Large Transport Aeroplanes”.
AIC 84/1992 (Pink 48) Dated 15 October 1992, does not mention in any shape or form that retracting flaps after landing is a means of keeping the LDR to a minimum. There is NO approved schedule I know of allows for this.

With the greatest respect to all F27 operators, I cannot see how this SOP has crept in as an approved method.

Somebody, somewhere, looks as if he thought it might work in theory so started teaching it.

I know I’ve asked before, but can ANYBODY gives me absolute proof this is an approved CAA or FAA method to determine LD requirements, and as a follow-on is written up as such in the FM ?

Cheers.

[Luftwaffle]

I don't fly F27s or anything nearly that big, but here's what, besides the owner's manual, I would look at in considering whether flaps should be retracted for braking.

The aircraft is stopped by two things, drag of air against the airframe, and friction of wheels against pavement. Drag is dependent on the shape of the plane and the airspeed. Friction is dependent on the coefficient of friction between the tyres and the runway surface, on the area of the tyre in contact with the runway, and on the weight resting on those tyres.

On most types, retracting flaps decreases aerodynamic drag and increases the weight on the wheels. The question is, do the flaps add more drag or more lift: which effect dominates at rollout speeds? If the manufacturer specifies use of flaps for a short field take-off, doesn't that mean that right up to climb-out speed that amount of flap is giving more lift than drag?

Well, if the braking efficiency were really poor (imagine a runway friction index of zero), then the weight on the wheels would be irrelevant and the contribution from drag would be the only thing stopping the plane. (Responses to pilots' prayers I will assume to be unaffected by flap setting).

If the aircraft is a millimetre over the runway with full flaps, just above Vso, then there is no weight on the wheels, and the brakes will be useless until the aircraft stops flying. In this situation, dumping the flaps will result in the wheels hitting the ground, and the aircraft will slow down much more quickly than it does while floating.

Somewhere between these two extremes is your aircraft. Because drag increases with speed more than lift does, I suspect that the only aircraft that shouldn't have flaps up for max braking are those with very similar flaps up and flaps down stall speeds.

I go by the manual. I know the manufacturer picked the method of braking that allowed them to boast the shortest landing distance, so I'm counting on that being the one most likely to keep me on the runway.

[ironbutt57]

same sop on the CV-580...same reason...fewer "square" tires as well....

[pterodactyl]

I am not certain of this but thinking back I recall that rudder effectiveness on the F27 was significantly affected by Flap positions beyond 16.5 which did disrupt airflow over the rudder. There was a very significant increase in VMCA at actual Flap settings above the certified position which I think was 16.5. This serves to confirm the reduction of rudder effectiveness at high Flap settings.
The F27 as I recall was quite controllable in a crosswind at touch down speed but there was a noticeable rudder deficiency during the ground roll in the region between 50 and 30 knots and this coupled with the pneumatic brakes with full rudder applied was a handfull.
Perhaps it was a desire to improve rudder effectiveness which led to this procedure but I do not recall it as an SOP.

[JVDS]

I fly the F-27 myself.

Couple things. Bringing up the flaps after landing will reduce the lift significantly, even if you have an aircraft equiped with spoilers. The lower part of the wing will still produce an upward force (lift) which is higher with flaps extended (Action=reaction). Maximum braking is only possible with as high as possible weight on the wheels. Therefor reducing flaps after landing to reduce the landing roll is a possibilty.

However, by bringing up the flaps you also decrease the aerodynamic breaking.

My opinion: I don't think it has a noticable effect on the landing roll regardsless of what procedure you use.

By the way, it is not a SOP in our company to retract the flaps after landing in order to reduce the landing roll.

Cheers, and happy landings!!

[Right Way Up]

With regard to 757 flap retraction, I wonder if its like the 747-400 where some of the leading edge devices retract after thrust reverse selection?

[Daysleeper]

could be a generational thing. Seem to remember the DC-3 was the same.

[thewarintheair]

We were trained to dump flaps on landing on extremely short strips in C-185's, not convinced it makes much difference but every little helps. Also you could put them away in less than a second, without looking so no danger issue. On large aircraft with lift spoiling devices my, non tecnical, opinion is that it is a total waste of time at a busy moment.

[bluepilot]

The F27 had a nasty habit of weathercocking in strong cross winds, (the 500 series more so due to the increased length) also the single nose wheel did not provide very much grip and control. In a very stiff x wind (29 kts was the limit i seem to remember) it was important to maintain full aileron into wind opposite rudder to prevent weathercocking, with flaps 40 the "barn doors" increased the problem so were retracted on landing so as to help with direction control, the secondary effect to increase weight on the landing gear to assist. Braking with full rudder was an art in itself! one knee up at your chin and the other leg fully extended, this coupled with the pnumatic brakes was a real hand (or foot) full!!

Air uk standard SOP was to retract the flaps on landing for the above reasons. I also know the crew involved with the incident you are referring too, If you hear their story first hand it is very frightning and sobering indeed, thank goodness only slight injuries to the crew and all returned to flying, all passengers were evacuated without injury as far as i can remember.

[stilton]

We used to retract the flaps to 25 after lowering the nosewheel on the 727. had very effective spoilers on that aircraft as well so I do not remember the rationale for doing this.

[411A]

Well....the aircraft manufacturer sure should know what procedures are best, especially as they designed and test flew the aircraft to certification.

According to Fokker (and yes I attended the factory ground school), as the company had just acquired two new machines...

The wing down method for crosswind landings gives excellent results, and retracting the flaps to 16.5 just after touchdown will give added rudder effectiveness, at slower speeds, and will avoid weathervane effects.

Also, taxying with the flaps still at 16.5 will avoid undesirable empanage vibrations.

It was...right in the flight manual, in black and white.

RTFB, for best results.
Gee, what a surprise.:uhoh: