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Short field landings

 

Short field operations present several difficulties for pilots who are not normally experienced with longer runways.

Short length is of course the main problem, especially if you fly a high performance single or multi-engine aircraft. Additionally, a short runway with obstacles at the approach-end creates a whole new hazard. Luckily, both short length and obstacle clearance can be addressed by adjusting the approach path.

But there is more to making a short field approach to landing than just the approach. Different technique is required for the touchdown and after-landing roll as well. So lets take a look at a method of making a short field approach successful.

The Approach

: The first step to landing at a short field is to realize it is indeed a short field.

I have never seen any rules of thumb for figuring that out, but I use the following personal rule: 1.0 minus (required landing distance, divided by the available runway).

If the result is less than .4 (40 percent) then I plan on a short field approach and landing. The way I figure it, if you have less than 40% of the runway available beyond what you need to get down and stopped, then you have a reduced chance of getting stopped if the approach, landing, or braking is screwed up.

That might be a little conservative for some, but I prefer to have the extra margin of safety for those unplanned eventualities. Anyway, once you’ve decided you have a short field, its time to determine obstacle clearance requirements.

Aircraft are certified for landing and takeoff distances to clear a 50 foot obstacle at the approach or departure end of the runway. However, if you fly a normal approach figuring on clearing that 50 foot obstacle at the approach-end the subsequent touchdown is going to be quite a ways from the end. So we make a steeper approach to 1) clear the obstacle, and 2) to touchdown earlier (closer to the approach end) on the runway.

However, since when has Mother Nature put a 50 foot limit on end of runway obstacles at small non-commercial airports? Also, if you do indeed have a 50 foot obstacle, it seems foolish to assume you can just barely clear it and achieve the POH’s performance estimate.

In fact, the obstacle probably needs to be cleared by 20 or more feet for safety (I use 50 feet for safety). The ideal angle of approach varies depending on the obstacles being cleared, but in general it’s probably slightly shallower than a power-off approach for the same aircraft and definitely exceeds the standard three degree glide path angle.

Many pilot suggest that approach angle is best controlled with power, and airspeed controlled with pitch. However, I find it easiest to control the angle with pitch and airspeed with power.

In either case, control airspeed at around 1.3 times the power-off full flaps stalling speed (this implies that full flaps should be used for this type of approach). Any slower will improve the landing distance in theory, but will eliminate the safety factor above stalling speed. Any faster will result in floating prior to touchdown.

The key to maintaining the desired approach angle is to keep the desired touchdown spot in the same location in the windscreen. Some refer to this method as the aim-point method.

If the spot appears to rise relative to the windscreen, the approach angle is increasing. If the spot appears to sink, the approach angle is decreasing. Either problem has serious ramifications for a safe landing.

Any increase in approach angle beyond the desired, increases the rate of descent and/or potential sink rate as the touchdown is neared. This gives the pilot less time to judge the flare and either a hard landing or balloon is a real possibility.

A shallower than desired angle of approach naturally leads to landing long, but also may lead to an inadvertent stall since you are already flying at lower airspeed and lower power than for a normal approach.

The key to the perfect short field approach is that power is variable, angle and airspeed are constant, and that changes in power usually require an associated change in pitch in order to maintain airspeed.

Touchdown

: Ideally, the touchdown from a short field approach occurs at the minimum controllable airspeed at an attitude that approximates the power-off stall without closed throttle.

If you have not flown at minimum controllable airspeed in a while, find yourself a qualified instructor and go practice it a few times prior to doing short field work.

Now for the touchdown; the key here is energy management. Put simply, in a correctly performed short field approach, there is minimal energy left for flare and touchdown. This means the flare occurs relatively quickly with touchdown almost immediately after reaching the nose-high landing attitude and closed throttle. Care should be taken not to close the throttle too soon as the sink rate will increase quickly; sometimes more quickly than the pilot can respond.

Throttle can be used to soften the touchdown if you should happen to misjudge the process, but care needs to be taken to immediately reduce the throttle to idle upon touchdown.

Touchdown occurs on the main wheels, followed by the nose wheel. Flat landings mean one of two things just occurred: 1) you had a lack of energy and just pranged it on, or 2) you had too much airspeed and forced it on.

Landing roll

: After touchdown, the landing rollout commences. At this point, the throttle should remain at idle and braking begun to minimize the ground roll.

The airplane should be stopped as quickly as possible, but consistent with safety and control considerations.

Generally, after a properly executed approach and touchdown, braking will be light but positive. Even if needed, heavy braking should be avoided early in the landing roll to minimize the possibility of skidding.

Some aircraft recommend that flaps be retracted after touchdown to increase braking effectiveness, but my recommendation is to leave them extended if possible to minimize the distraction of retracting them. There have been many cases of loss of control after touchdown as a result of fooling around with the flaps!

The landing roll can be shortened even more by using full aerodynamic braking. This is the practice of deflecting the elevator or stabilator full up as the aircraft decelerates during the ground roll. As the aircraft decelerates, increase back-pressure slowly, all the way to full aft.

I would not recommend trying to keep the nose off the ground for additional aerodynamic braking effect, as loss of control becomes more likely.

Safety considerations

: Pilots are salvagers by nature. We "salvage" bad landings and turn them into acceptable landings all the time. However, with short field landings, safe salvaging is often next to impossible, so consider a go-around if it gets screwed-up.

Since a go-around may be needed at a split-second, keep your hand on the throttle throughout the approach to landing. Remember to compensate for crosswinds in the same way you would for a normal landing, except also remember that you’re slower so you’ll need more crosswind control for a given wind condition.

When planning to land on a really short runway, check the performance figures for takeoff as well. The landing distance is typically shorter than takeoff distance for the same conditions. After all, you don’t want your aircraft to become the airports newest permanent static display because you don’t have the room to takeoff again!

Prior to landing, pump the brakes a couple of times to make sure that you still have pressure in the lines. You don’t want to find out a brake has gone bad after touchdown on a short runway!

And finally, remember that a short field landing need not be firm. Performed correctly, this type of landing can be just as smooth as a normal landing.

This month’s Pilot Primer is written by Donald Anders Talleur, an Assistant Chief Flight Instructor at the University of Illinois, Institute of Aviation. He holds a joint appointment with the Professional Pilot Division and Human Factors Division. He has been flying since 1984 and in addition to flight instructing since 1990, has worked on numerous research contracts for the FAA, Air Force, Navy, NASA, and Army. He has authored or co-authored over 180 aviation related papers and articles and has an M.S. degree in Engineering Psychology, specializing in Aviation Human Factors.