WIND ADDITIVES AND LANDIND SPEED
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Thank you for your feedback.
a) On what speed the landing performance computation is based on?
On Vref (Vref+5/-0, Vref+20/15 …etc?) or on touchdown speed?
Extra speed (due to wind additives) + residual thrust when closing the thrust levers (due to longer spool down time) + the ground effect ==> increase the chance to float (due to extra lift). In order to reduce the “floating” you have to reduce the extra lift, thereby you have to reduce the speed (lift is proportional to the square of the speed).
b) Why aircraft manufacturers didn’t use/recommend the use of thrust reversers to reduce the “floating”?
c) Is there a risk for aircraft or engine limitation/problem…etc?
d) Is there a risk of “floating” for prop aircraft during the flare? I am assuming they can use the props as thrust reversers to reduce the speed and the lift during the flare.
Feedback appreciated
a) On what speed the landing performance computation is based on?
On Vref (Vref+5/-0, Vref+20/15 …etc?) or on touchdown speed?
Extra speed (due to wind additives) + residual thrust when closing the thrust levers (due to longer spool down time) + the ground effect ==> increase the chance to float (due to extra lift). In order to reduce the “floating” you have to reduce the extra lift, thereby you have to reduce the speed (lift is proportional to the square of the speed).
b) Why aircraft manufacturers didn’t use/recommend the use of thrust reversers to reduce the “floating”?
c) Is there a risk for aircraft or engine limitation/problem…etc?
d) Is there a risk of “floating” for prop aircraft during the flare? I am assuming they can use the props as thrust reversers to reduce the speed and the lift during the flare.
Feedback appreciated
Certificated landing performance (AFM) is based on Vref; - CS/FAR 25.125
Operational landing performance (QRH) may be based on a higher speed than Vref; e.g. many manufacturers use Vref + 5 as a baseline, and for autoland. Distance corrections should be applied to the AFM performance for any difference from Vref: – AC 91-79.
In normal operation, residual thrust should be removed during the flare. It will only be a small component of any increased distance (float) in comparison with high airspeed or a tailwind. Lift per se, does not create the ‘float’; the pilot can still land the aircraft at a higher airspeed at the required position, but the higher energy has to be dissipated during the landing rollout.
Thrust reverse is not normally included in AFM performance due to reliability, consistency, and usability issues; - CS 25.125 (c) and (g).
Most manufactures recommend the use of reverse on the ground; however the extent of this is often left to the judgement of the crew based on the conditions. Thus this decision is subject to the variability in human performance.
The problems above could be considerably exacerbated if airborne use of thrust reverse was considered; - CS 25.933 (a) (2), in flight use.
Propellers slipstream may increase lift, but as above, the aircraft can still be controlled to reduce float and land at the required position, albeit at a higher speed. Speed is the dominant issue.
The regulations for propeller driven aircraft differ from jets, but use of ‘reverse’ (discing) in the air involves other risks, and depending on aircraft type, may affect pitch control.
The better defence against landing overruns is to fly speed accurately, avoid tailwinds (higher ground speed), land at the planned position, and select retardation devices promptly. Distance corrections should be made for planned higher speeds, touchdown position, height over threshold, tailwind, and runway condition – wet … contaminated.
CS 25 http://www.easa.eu.int/agency-measur...dment%2011.pdf
AC 91-79 Runway Overrun Prevention
Operational landing performance (QRH) may be based on a higher speed than Vref; e.g. many manufacturers use Vref + 5 as a baseline, and for autoland. Distance corrections should be applied to the AFM performance for any difference from Vref: – AC 91-79.
In normal operation, residual thrust should be removed during the flare. It will only be a small component of any increased distance (float) in comparison with high airspeed or a tailwind. Lift per se, does not create the ‘float’; the pilot can still land the aircraft at a higher airspeed at the required position, but the higher energy has to be dissipated during the landing rollout.
Thrust reverse is not normally included in AFM performance due to reliability, consistency, and usability issues; - CS 25.125 (c) and (g).
Most manufactures recommend the use of reverse on the ground; however the extent of this is often left to the judgement of the crew based on the conditions. Thus this decision is subject to the variability in human performance.
The problems above could be considerably exacerbated if airborne use of thrust reverse was considered; - CS 25.933 (a) (2), in flight use.
Propellers slipstream may increase lift, but as above, the aircraft can still be controlled to reduce float and land at the required position, albeit at a higher speed. Speed is the dominant issue.
The regulations for propeller driven aircraft differ from jets, but use of ‘reverse’ (discing) in the air involves other risks, and depending on aircraft type, may affect pitch control.
The better defence against landing overruns is to fly speed accurately, avoid tailwinds (higher ground speed), land at the planned position, and select retardation devices promptly. Distance corrections should be made for planned higher speeds, touchdown position, height over threshold, tailwind, and runway condition – wet … contaminated.
CS 25 http://www.easa.eu.int/agency-measur...dment%2011.pdf
AC 91-79 Runway Overrun Prevention
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Boeing give a hint under the adverse weather section of the FCOM when landing with ice on the airframe and recommend adding 10 knots to Vref plus other additives already applied - up to a max additive of 20 knots. Boeing goes on to say "bleeding off the 10 knots (ice additive) below 200 ft. This would suggest that the deliberate bleeding off the half HW additives should start at 200 ft. It is a tenuous example, but Boeing tend to be vague in such areas.
But I cant find the info in my airline fcom supp info.
Could someone paste and copy please?
Thanks.
But I cant find the info in my airline fcom supp info.
Could someone paste and copy please?
Thanks.
Could someone paste and copy please?
Thanks.
"Note: To prevent increased landing distance due to high airspeed, bleed off airspeed in excess of VREF+5 knots + gust correction when below 200 feet AGL. Maintain the gust correction to touchdown."
My copy of the FCOM is out of date, so check with latest revision number.
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Interesting, just checked my FCOM (newly released company version valid on january 1st) and the only note referring to cold weather approach and landing is to use normal flaps and speed additives except for non normal situations requiring flaps 15 (not approved as normal landing flap setting) in which case Vref ICE has to be used (Vref 15 +10kts). No other speed additive is mentioned at all.
Could there be an FCOM difference for those planes which have flaps 15 as normal landing flap setting and those that don't?
Could there be an FCOM difference for those planes which have flaps 15 as normal landing flap setting and those that don't?
