FLAP MALFUNCTIONS

Taken, in part, from article by Barry Schiff, and from “Aerodynamics for Naval Aviators”

Flaps-

High lift devices used to increase maximum lift coefficient for low speed flight.

Produce effect of large amount of camber added well aft on wing.

FLAP MALFUNCTIONS

• Purpose is to increase safety in takeoffs and landings (by reducing required airspeed)

• Partially-deflected flaps used on large aircraft for all takeoffs

• Partially-deflected flaps sometimes used on GA aircraft for short-field takeoffs

• Usually used by all aircraft for landing

FLAP MALFUNCTIONS

• True for most airplanes-– First 50% of flap deflection causes more

than half the total change in maximum lift

– Last 50% of flap deflection causes more than half the change in total drag

FLAP MALFUNCTIONS

• Cessna 150-– Stall speed at 20 degrees flaps just 1 kt

higher than stall speed at 40 degrees flaps!

– For students, some CFI’s use 20 deg as standard, to increase safety in case of go-around

FLAP MALFUNCTIONS

• Malfunctions-– Multi-engine student and CFI doing

touch & goes; after normal liftoff, immediately rolled right and crashed inverted

– Left flap found full-down; right flap fully retracted!

FLAP MALFUNCTIONS• Flap asymmetry results in roll to side with

least flap deflection

• Certification requires safe flight characteristics with one fully deflected flap, and the other fully retracted!

• Un-commanded roll catches pilot off-guard; some aircraft can be visually checked, some cannot (Cessna twins)

FLAP MALFUNCTIONS

• Roll must be countered with (lots of) opposite aileron, and substantial (cross-control) rudder (to counter flap drag)

• Full aileron may be required to maintain wings level during landing - do not attempt crosswind landing

FLAP MALFUNCTIONS

• Large potential stall speed difference between wings; if approach flown too slowly, snap-roll type dynamics can result, with fatal spin!

• Conduct approach at least 30% faster than flaps-up (clean) stall speed

• Greater runway length required for landing!

• Fly onto runway - do not flare (stall)

FLAP MALFUNCTIONS• Total flap failure more common (e.g. flap

motor in T-34)• Requires substantially more runway to land• Aircraft nose-high at reduced speeds in pattern• Nose attitude can restrict view of traffic and

runway• Uncomfortable attitude may lead to

abnormally high approach speed

FLAP MALFUNCTIONS

• Altitude more difficult to lose without flaps; diving to lose altitude just increases airspeed

• Fly wider , longer traffic pattern

• Aircraft may tend to float excessively during landing

FLAP MALFUNCTIONS

• Retraction failure– Potential leads some pilots to wait until landing

assured before extending flaps– Go-around may be impossible, depending on

amount of deflection– On touch & goes, potential of retraction failure

requires visual confirmation of flap position

FLAP MALFUNCTIONS• SAFETY CHECKLIST

– Operate flaps during preflight– Stay within flap operating speed limits– Check lubrication– When electric flaps fail, check circuit breaker– Do not rely on flap position indicator– Don’t taxi on unimproved surfaces with flaps

extended– Don’t extend all at once; do it incrementally