Fying with Defective Instruments

Here is an article written by Bob Pirie, one of our instructors, after one of our gliders had a problem with it’s ASI.
A salutary reminder to all of us from Bob and Phil’s experience.
Despite an ASI needle ‘tweaking’ during d.i. inspection and thus giving the impression of working, I have known several of instances of gliders (usually having been parked outdoors for several days) accumulating water in ASI tubes and not working – but the BobBug obviously had a similar effect.
As well as the importance of taking preventive measures while parking up a glider for the night, and then carrying out a thorough d.i. inspection before the next flight, being familiar with the characteristics of the glider you’re flying is vital if things do go wrong (which the pilot-in-charge fortunately was in the instance reported).
All pilots should be able to identify and cope with an ASI malfunction, bearing in mind that it may not stop working altogether, but may simply mis-read. Both can be very disconcerting if not scary, and the latter downright dangerous if it goes unrecognised.
I would suggest that anyone converting to a ‘new’ type of glider (or whose knowledge of the glider they fly regularly may be a bit rusty), should prepare themselves for an ASI failure by, firstly, getting a briefing from an instructor. Then, once they have gained a basic level of familiarity with the glider’s handling characteristics (and provided they have plenty of height – and with one eye on the serviceable ASI), they experiment with attitude/speed/airbrake/trim etc. and most importantly stall warning symptoms.
Next – not necessarily on the same flight, and again with plenty of height (after a thermal climb,say, but not actually in a thermal) – configure the glider for landing including (if applicable) lowering the wheel, selecting landing flap and trimming for approach speed. Then try a dummy approach for a few seconds. But before commencing this brief descent, do a clearing turn and have a good lookout for other aircraft – especially beneath you.
Make and retain a mental note of what a ‘normal’ approach attitude looks like, the trim position and the way the glider sounds and feels. Then you’ll stand a better chance of staying ahead of the game if and when your ASI does let you down.
Do not put yourself at risk of running out of height when doing this exercise. Afterwards, unless you’re intending to actually land, remember to retract your wheel before continuing with the flight, thus reducing the risk of inadvertently retracting it rather than lowering it when you do eventually configure the glider for a real landing.
Bob Pirie