Proficient Pilot: What's All The Flap About

I reached down for the long handle between the seats and pulled it up to the first notch, just the way I did when flying an elder 172 with manual flaps.

The Italian instructor to my right gave a quizzical look and asked, “Tell me, signor. Why are you pulling on the parking brake?” He then explained that the flap handle was on the ceiling and needed to be pulled down to extend the flaps. He also said the Oscar would be easier to land in the crosswind using only partial flaps.

This latter advice caused me to later question the conventional wisdom of always landing with full flaps. Everyone knows the advantages: reduced floating in the flare, reduced touchdown speeds, shorter landing distances, and less wear and tear. There are numerous occasions, however, when it is desirable to land using only partial flaps, especially when long runways are used.

For starters, it usually is easier to land a tricycle-gear airplane when using partial flaps (especially with a forward center of gravity). This is because deploying full flaps results in a lower nose-down attitude during the approach, and this can make it more difficult to raise and hold off the nosewheel during touchdown. Some of the prettiest and smoothest nose-high landings are made using only partial flaps.

Some airplanes—such as low-wing Piper singles—are particularly difficult to land while holding off the nosewheel. This makes these and other such aircraft more vulnerable to wheelbarrowing and loss of directional control. One solution is to land using partial flaps.

Some argue that using less than full flaps reduces stall protection. This is seldom significant. The last 10 or 20 degrees of flap deflection rarely reduces stall speed by more than a knot or two (if that much). For example, decreasing the flap extension of a Cessna 182RG from 40 to 20 degrees increases stall speed from 41 to only 43 knots.

There are some advantages to making a landing approach with less than full flaps. One is that go-arounds (VFR) and missed approaches (IFR) are simplified, safer, and result in improved initial climb performance. When using partial flaps, a pull-up can be initiated without retracting flaps until reaching a safe altitude. On the other hand, some airplanes cannot climb at all with flaps fully extended (depending on weight and density altitude). This requires that the pilot partially retract the flaps close to the ground and cope with changes in pitch and elevator stick forces at a time when workload is already high.

Another advantage is that the reduced drag of a partial-flap approach makes the airplane less susceptible to wind shear; there is more excess power available with which to combat airspeed and altitude losses.

Also, an inadvertent stall during a partial-flap approach is tamer than when using full flaps. This is because less power is being used at such a time. A power-on stall with flaps fully extended typically produces the largest, quickest, and most unexpected attitude changes. It also results in a greater altitude loss.

My favorite reason for a partial-flap approach is that the airplane glides farther in the event of an engine failure. Yes, the flaps can and probably should be retracted at such a time, but some pilots might have difficulty coping with the unexpected trim changes and momentary increase in sink rate that would occur at such a critical time.

With respect to crosswind landings, arguments can be made for and against the use of full flaps. With flaps fully deployed, the airplane has a greater surface area against which a strong wind can blow once the aircraft is on the ground, which denigrates directional control. This is why some pilots retract the flaps immediately after touchdown in a blustery crosswind. This serves the added benefit of increasing stall speed, which makes it less likely that the airplane will inadvertently balloon due to a strong and sudden gust after landing.

Interestingly, the use of full flaps makes it easier to control roll during gusty approaches. With flaps extended, air “blocked” by the flaps spills outboard toward the ailerons, thus improving their effectiveness.

This argues that using full flaps for landing is not a cut-and-dried issue. I concede, however, that the parking brake should not be used until coming to a stop.

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