Wednesday, 26 October 2016
FIXED-WING LANDING ACCIDENTS
Acknowledgements: GASCO/Nigel Everett
Landing accidents form the greatest proportion of total accidents reported by GA aircraft, and we may be sure that there are also many other landings which only just escape injury or damage and thus are not reported as accidents.
The good news is that they are seldom fatal, and so the usual outcome is damage to aircraft but little personal injury, although as a result the cost of higher insurance premiums can be considerable, as can the loss of self-regard and confidence on the part of those involved.
Employing the three disciplines described below will greatly reduce the likelihood of a landing accident if done right, or greatly increase it if done wrong.
1. Established on finals
In the airline world there is a minimum height requirement for becoming fully-established on final approach, and we GA pilots should adopt the same discipline voluntarily. Decide upon a minimum fully-established height, recommended by Jeremy Pratt to be 300 ft. but taking account of your own personal parameters in terms of experience and confidence, and ensure that you have done everything needed to prepare for landing by the time you attain that height. After which do not attempt to correct anything which is not as it ought to be for maintaining the fully-established condition – airspeed, trim, configuration, final checks, ATC clearance if appropriate etc. If after that point any adjustment is needed GO AROUND! This will greatly reduce your chances of a landing accident.
2. Approach speed
The accepted approach speed for a powered light aircraft is 133% of stall speed in landing configuration and at current weight, though some prefer 125% as it gives a shorter float and landing run - but also of course less margin for error! In windy conditions you should add a “gust factor” equating to 50% of the difference between current wind strength and gust speed. High speed on landing is likely to result from a high speed approach.
If flying a tail-dragger a high speed landing is rarer as a high-speed approach will not achieve an acceptable 3-point touchdown. The problem is more acute with a tricycle geared aircraft, as the pilot can “get away with” a 3-pointer as long as the nose-wheel doesn’t make contact significantly ahead of the main wheels. Thus we frequently see a nose-wheel aircraft arriving too fast and touching down flat after very little holding off, which means that the aircraft is still partially flying. Many landing accident reports reveal problems in the roll-out rather than the touchdown, because the aircraft landed whilst flying so that the brakes and nose-wheel did not function as expected. This is generally avoidable if the pilot does not allow the aircraft to touch down until it has run out of flying speed.
Studies have shown that the incidence of accident is inversely proportional to the amount of flap deployed. More flap = fewer accidents so the advice is to use more to stay safer, because you will achieve a slower touchdown with less reaction to gusting, and a more “draggy” and stable aircraft. The transition from airborne to ground borne is risk-inherent, and the use of flaps helps to minimise the duration of the landing phase and to improve control during it.