Flight Instrument Malfunctions
Instrument failures can result from careless maintenance practices and from internal or external causes. An example of careless maintenance is removal and replacement of the airspeed indicator but failure to connect the instrument correctly to pitot and static lines. A pitot tube clogged by insects or water ingress is an example of an external cause of instrument failure.
Pilots should always be aware of the glider’s normal attitudes for all flight regimes. Then, when presented with an instrument failure or erroneous indication, the pilot has a general sense of the glider’s normal attitude from outside flying cues to make a safe return and landing. Judging the altitude or airspeed of the glider without the guidance of instruments should not constitute a panic in the cockpit as many pilots can make precision approaches and landings without the use of an altimeter. In fact, many older and vintage gliders do not require an operational altimeter in the cockpit.
Airspeed Indicator Malfunctions If the airspeed indicator appears to be erratic or inaccurate, fly the glider by pitch attitude. Keep the nose of the glider at the proper pitch attitude for best glide or minimum sink airspeed. Additional cues to airspeed include control “feel” and wind noise. At very low airspeeds, control feel is very mushy and wind noise is generally low. At higher airspeeds, control feel is crisper and wind noise takes on a more insistent hissing quality. The sound of the relative wind can be amplified and made more useful in airspeed control by opening the sliding window installed in the canopy and by opening the air vent control. During the landing approach, maintain adequate airspeed using cues other than the airspeed indicator. Fly the approach with an adequate margin above stall airspeed. If conditions are turbulent or the wind is gusty, additional airspeed is necessary to penetrate the convection and to ensure adequate control authority. If in doubt, it is better to be flying 10 knots faster than optimum airspeed than it is to be 10 knots slower.
Altimeter failure may result from internal instrument failure or from external causes, such as water ingress in the static lines. Regardless of the cause, it is important to maintain sufficient altitude to allow a safe glide to a suitable landing area. During the approach to land without a functioning altimeter, it is necessary to rely on perception of maintaining a safe gliding angle to the target landing area. The primary risk to safety is entering the approach from an altitude that is lower than normal. It is better to enter the approach from a normal height, or even from a higher-than-normal height. During the approach, judge the angle to the target area frequently. If the angle is too steep, apply spoilers/ dive brakes to steepen the descent path. If necessary, apply a forward slip or turning slip to lose additional altitude. If the approach angle is beginning to appear shallow, close the spoilers/dive brakes and, if necessary, modify the approach path to shorten the distance necessary to glide to make it to the target landing area.
Static line contamination affects both the altimeter and the airspeed indicator. If it is suspected that either instrument is malfunctioning because of static line contamination, remember that the indications of the other instrument(s) connected to the static line may also be incorrect. Use the external cues described above to provide multiple crosschecks on the indications of all affected instruments. If in doubt about the accuracy of any instrument, it is best to believe the external cues and disregard the instrument indications. After landing and prior to the next flight, have an aviation maintenance professional evaluate the instrument system.
It is essential that a glider pilot be familiar with the procedures for making a safe approach without a functioning airspeed indicator or altimeter. Being accompanied by a glider flight instructor during the flight review provides an excellent opportunity to review these procedures.
Variometer failure can make it difficult for the pilot to locate and exploit sources of lift. If an airport is nearby, a precautionary landing should be made so the source of the problem can be uncovered and repaired. If no airport is nearby, search for clues to sources of lift. Some clues may be external, such as a rising smoke column, a cumulus cloud, a dust devil, or a soaring bird. Other sources are internal, such as the altimeter. Use the altimeter to gauge rate of climb or descent in the absence of a functioning variometer. Tapping the altimeter with the forefinger often overcomes internal friction in the altimeter, allowing the hand to move upward or downward. The direction of the movement gives an idea of the rate of climb or descent over the last few seconds. When lift is encountered, stay with it and climb.
Compass failure is rare, but it does occur. If the compass performs poorly or not at all, cross-check current position with aeronautical charts and with electronic methods of navigation, such as GPS, if available. The position of the sun, combined with knowledge of the time of day, can help with orientation also. Being familiar with section lines and major roads often provides helpful cues to orientation and the direction of flight.
Glider Canopy Malfunctions
Glider Canopy Opens Unexpectedly
Canopy-related emergencies are often the result of pilot error. The most likely cause is failure to lock the canopy in the closed position prior to takeoff. Regardless of the cause, if the canopy opens unexpectedly during any phase of flight, the first duty is to fly the glider. It is important to maintain adequate airspeed while selecting a suitable landing area.
If the canopy opens while on aerotow, it is vital to maintain a normal flying attitude to avoid jeopardizing the safety of the glider occupants and the safety of the towplane pilot. Only when the glider pilot is certain that glider control can be maintained should any attention be devoted to trying to close the canopy. If flying a two-seat glider with a passenger on board, fly the glider while the other person attempts to close and lock the canopy. If the canopy cannot be closed, the glider may still be controllable. Drag is higher than normal; when flying the approach, plan a steeper-than-normal descent path. The best prevention against unexpected opening of the canopy is proper use of the pretakeoff checklist.
Broken Glider Canopy
If the canopy is damaged or breaks during flight, the best response is to land as soon as practicable. Drag increases if the canopy is shattered, so plan a steeper-than-normal descent path during the approach.
Frosted Glider Canopy
Extended flight at high altitude or in low ambient temperatures may result in obstructed vision as moisture condenses as frost on the inside of the canopy. Open the air vents and the side window to ventilate the cabin and to evacuate moist air before the moisture can condense on the canopy. Descend to lower altitudes or warmer air to reduce the frost on the canopy. Flight in direct sunlight helps diminish the frost on the canopy.