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the gremline digest — the constant aspect approach
Forced Landings in Light Aircraft — The ‘Constant Aspect’ Approach
If you have arrived here from the preceding article on forced landings in light aircraft, carry on reading. If not, we suggest that that you study our previous piece before proceeding. Click Here.
The diagram is self-explanatory if you study it step by step but perhaps it needs to be emphasised that the IAP is held closer to the aircraft fuselage than to the wingtip throughout the pattern. It is also worth noting that there is no mention of aircraft altitude after leaving the “high key” point at the beginning of the exercise. The “high key” position is purely a training aid for use during PRACTICE forced landings and is not an essential part of the pattern for a real forced landing. The pattern is best visualised as flying the aircraft around the surface of an irregular cone which has its apex at the IAP and its angle determined by the aircraft’s gliding angle. One may join this cone at any position and height relative to the IAP and, if necessary, fly several orbits while losing height – or less than one orbit if short of altitude. There is no rigid pattern over the ground. This varies automatically to take account of wind velocity (Velocity = speed and direction) and rate of descent, and may be a continuous gentle curve. The angle of the cone is determined by the Sight Line Angle, as defined below.
The concept of Sight Line Angle (SLA) needs a diagram to make it absolutely clear, so here is my second little picture.
The Sight Line Angle is the angle below the
horizon of the INITIAL AIMING POINT. It doesn’t matter what size this
angle is in degrees or radians or anything else. You select your IAP while
gliding abeam your chosen field, or sooner if possible, and note the angle
subtended below the horizon. If this SLA begins to INCREASE then you are
OVERSHOOTING your IAP. If the SLA begins to DECREASE then you are
UNDERSHOOTING your IAP. Think about the concept for a while and get the idea
fixed in your mind. In fact, you already knew this, but may not have
consciously recognised the fact. If the SLA is increasing then you are
closing in on your IAP. If the SLA is decreasing then you are drifting away
from your IAP. That’s all there is to think about.
Your touchdown point will have been chosen to give
you at least a few yards inside the near hedge so it doesn’t matter if
you undershoot or overshoot by a couple of yards. Do not grope for the
ground. Rotate the aircraft into the landing attitude and then land. You may
notice a slightly different feel on the rudder and elevator because of the
lack of prop wash over the controls. Your airspeed should be right for
landing so put it on the ground in the correct attitude for your type. No
nosewheel type takes kindly to landing nosewheel first and the only way you
can do that is to be either too fast or fly into the ground without any
flare. “Wind shear” seems to be the currently favoured excuse for
bad landings. Bad landings result from bad approaches flown by careless
pilots. Once you are on the ground apply maximum safe braking. The technique
varies from type to type, but probably involves holding the elevator control
well back as the brakes are applied. Locked wheels offer less retardation
than braked rotating wheels, so try not to lock the wheels. Beware of harsh
braking on wet grass. Don’t forget to steer the aircraft until it comes
to a full stop - or the far hedge! If you are going to hit the far hedge,
have a go for a gateway or the gap between two trees. It’ll make a
great picture to hang in the Flying Club.
Text and Photographs © 2008 Gremline & Hill House
Publications, unless otherwise stated.
Text and Photographs © 2008 Gremline & Hill House Publications, unless otherwise stated.