Landing Distance Calculations with Reversers
Landing Distance Calculations with Reversers
(OP)
Does any body know if Boeing factors in reverse thrust
when they calculate landing distances over the 50 ft
obstacle for the 737?
FAR Part 25.125(f) states you have to assume an engine
out condition upon landing so I always understood
reversers were never part of the stopping distance
equation.
Further that the main justification for reversers was
economic, savings on tires and brakes.
when they calculate landing distances over the 50 ft
obstacle for the 737?
FAR Part 25.125(f) states you have to assume an engine
out condition upon landing so I always understood
reversers were never part of the stopping distance
equation.
Further that the main justification for reversers was
economic, savings on tires and brakes.





RE: Landing Distance Calculations with Reversers
Thrust reversers are much more efficient than brakes alone in slowng down the airplane that is why they are used. They generate about 80% of the forward engine thrust. brakes are used at the end of the landing roll.
Regards
Dave
RE: Landing Distance Calculations with Reversers
CESSNA1
So even with malfunctioning reversers, the 737 at
Chicago Midway should have been able to stop on
the runway assuming the pilot was flying otherwise
by the numbers, ie. at a 50 ft height over the end
of the runway, flying the approach at Vref plus
any adjustment for gusts, and increasing the Flight
Manual Landing Distance as necessary for snow/ice
on the runway.
Would that be your conclusion?
RE: Landing Distance Calculations with Reversers
Regards
Dave
RE: Landing Distance Calculations with Reversers
RE: Landing Distance Calculations with Reversers
Very basically, for dispatch purposes, thrust reverse cannot be included in the stopping distance, as well as only one half of head wind and 150% of tail wind component. There are other items involved such as designation airport runway slope (uphill or downhill), pressure and temperature different from standard at intended time of landing, as well as intended landing weight. From this information you must be able to land in 60% of your designation airport’s runway, as per FAR 121.195 for dry runway, or 115% for wet runway. FAR 121.195 are for dispatch only; if things change in flight, you can use 100% of runway if you have to. Note: AC 121.195 explains certification requirements for wet runways.
That is how it works most of the time, but there are times when things line up to cause problems. The book Fly the Wing lists some rule of thumbs that show differences from an ideal, dry runway:
Antiskid inoperative – add 75% from max antiskid breaking,
Ground spoiler inoperative – add 25%,
Reversers inoperative– add 10-20 %.
If you cross threshold at 100 feet instead of 50 – add 900 feet to touchdown distance.
1% increases in speed over correct V(ref) – add 2% change in landing roll.
1% increases from max landing weight - add 1% change in landing roll.
Add other factors like ATC, maintenance problems etc. that may be involved.
Most accident of this nature have several factors involved, both active and latent. There is usually no single cause. After an accident the media runs around trying to find “the cause” or someone to blame. Then they lose interest and move onto something else. It is when some of the factors above and others, line up, with no defences that accidents occur.
The following site is from Transport Canada’s site and shows that when landing on ice, the stopping distance can increase substantially without reversers as was discussed in previous post.
http://
The following site has a calculator for the B737 landing distance.
http://www.b737.org.uk/landing_distance.xls