Corroded elevator control tube fractures on a Glasflügel 304S during aerotow
A pilot was seriously injured and his Glasflügel 304S substantially damaged when the elevator control tube fractured on an aerotow launch at Briggs and left him without pitch control. The glider came off the towline with the tow plane about 90 m up, turned left and landed wings level, and the tailboom separated from the fuselage. The tube had corroded along its whole inner surface: water could get into it, but with no drain hole at the bottom it could not get out. It had already split lengthwise near the top, a crack the mechanic would have seen had he removed the rubber boot at the inspection 24 days earlier.
- No drain hole in the control tube: The elevator control tube in the vertical stabilizer had no drain hole at its lower end, so water that entered it could not get out.
- Corrosion thins the tube from within: Water probably entered through a witness hole near the top, or as moisture carried in by humid air, and corroded the tube along its entire inner surface, thinning its wall.
- Inspection 24 days before misses it: The tube had already split lengthwise near its upper end. The report judges the mechanic would have seen it readily had he removed the rubber boot at the condition inspection.
- Control tube fractures on the launch: During the launch the weakened tube fractured in overstress near the clevis fitting, and the pilot no longer had control of the elevator.
- Off the towline, tow plane at 90 m: The glider came off the towline with the tow plane about 90 m above the runway, and turned left.
- Tailboom separates on landing: The glider landed wings level. The tailboom separated from the aft fuselage and the pilot was seriously injured. The tow plane and the towline were undamaged.