Main Pin Securing Device
Info: DG-400 in-flight accident 1999, pilot Fred Jacobs
In May 1999 an accident happened in the US with a DG-400. The left wing separated from the glider in flight. Fortunately the glider was so high that the pilot Fred Jacobs could rescue himself bailing out.
The pilot reported that he heard a loud bang and that he could see, that the left wing pointed upwards approximately 20°. Then the glider speeded up and the pilot decided to bail out.
During investigation of the wreckage it was noticed that the complete securing device for the right hand main pin has separated from the fuselage shell including the glass fiber laminate which fixes the aluminum square tube of the securing device to the shell. If the securing device came loose in flight before the wing separated or if the spar end of the loose wing hit off the device is unclear. As the left hand spar end is located in front there is a high possibility that it hit the securing device.
If the main pin is not secured it may slide to the front due to movements of the spar ends. However the forces in this direction are very small as long as the pin is still inserted into both spar ends. The forces can't separate an undamaged securing device from the fuselage shell.
So there are only 2 possibilities:
a) the main pin was not secured,
b) the securing device has been damaged by a high load prior to the accident.
Due to this accident the FAA has ordered to check the securing devices on DG-400’s in the US. On one DG-400 it was found that the glass fiber laminate came partly loose below the aluminum bracket. However the photographs of this area showed residues of gluing material below the loose laminate which means that someone has glued something to the fuselage shell which has been broken away later on. It is likely that doing this also the laminate of the securing device was broken loose.
It is our opinion and the opinion of LBA and FAA that the person which rigs the glider must notice if the securing device is loose, as one has to pull out the locking pin with a certain force to allow the main pin handle to be placed behind the aluminum bracket of the securing device. This means, that you do an integrity test of the device each time you rig the glider.
Recommendation:
We recommend to all owners of DG single seaters (all have the same device except for the first DG-100’s) to have a closer look to the device when rigging the glider the next time.
If you detect a loose securing device please inform the DG factory and don't operate the glider before a repair was done.
Bruchsal, 2000-03-07 Wilhelm Dirks