The BGA’s latest edition of Managing Flying Risk has introduced a section on cartwheel accidents in both the winch and aerotow sections. There have been several cartwheel accidents during winch launches due the rapid acceleration involved, but including the warning in the aerotow section is a little unexpected. The Safe Aerotowing leaflet says that cartwheel accidents on the ground run of the aerotow are unlikely as there is insufficient energy. The Managing Flying Risk document says:
Cartwheeling accidents - predominantly to experienced pilots –happen as a result of not releasing the cable if the wing drops during the ground run. Cartwheel accidents have occurred during aerotow launches. If the wings cannot be kept level before take-off, release before the wing touches the ground.
This is a curious choice of words as there have been no such accidents in the UK during the 5 million aerotows undertaken since 1974. There was one aerotow ground run cartwheel accident in France in 2014, which I will describe in more detail later. Cartwheel accidents are a serious threat on winch launches, but much more unusual during the early phase of aerotow.
The most serious aerotow accidents are vertical and lateral upsets once the glider is airborne. These accidents can be fatal for the tug pilot. Thankfully although easily done, these are relatively rare. The commonest accident involves a ground loop by the glider after a wing drop on the ground run. Some gliders/pilots are more prone to dropping a wing than others. At our club, the K21’s wings are quite easy to keep level, while the Astir is much more of a challenge. The factors making a wing drop more likely are:
Limited experience of the glider
Glider fitted only with a C of G hook
Short wing span glider with washout
Short aerotow rope
Prop wash hitting a wing
Turbulent air in the take off area
Wing tip runner releasing the tip too early or holding it back
Most of the above factors kick in when our pilots convert from the K21 to the Astir. Even in the most favourable conditions, the Astir ailerons are less effective than the K21s during the ground run, so you have to use much more control input to keep the wings level. It is quite common to see novice Astir pilots get caught out and the wing touches the ground before they can release. Sometimes they report that they hadn’t noticed that the wings had touched the ground and so just carried on trying to get the wings level. Many experienced pilots have been seen dropping a wing and then picking it up and carrying on… is this a case of Do as I say not as I do? Is the wing on the ground inherently a catastrophic thing?
Wing Drops During the Ground Run on Aerotow