Posted for Gary Casey <glcasey@adelphia.net>:

 Normally, with a main gear (like on a Cessna) the assumption is that  the
only load on the main downlocks is the weight of the gear  itself.  When on
the ground the weight of the aircraft holds the gear  in the "down" position.
 In order to retract the gear initially goes  down - straight down on a
Cessna, but I don't know the details of the  geometry on the LIV - but
alternatively, the aircraft could be lifted  to allow the gear to retract.
 Remove much of the weight on the  mains, and then probably double the thrust
and the loading on the  downlocks is probably more than they are designed to
withstand, the  plane lifts as the gear folds.  Artificially restraining the
wheels  with chocks shouldn't be a problem as the limit is the coefficient of
 friction to the ground, probably higher with a locked wheel than  between the
block and the ground, although one block flying out might  have put an impact
load on the other gear, which could have started  the chain reaction.  I'd put
my bet on the lack of thought in  planning the test as being the root cause.
 If one is going to  restrain a plane in a test like that, doing it closer to
the center  of thrust would reduce the abnormal loading on all components.
 I'd  vote for restraint cables attached at the root of the gear legs.
 
 Gary Casey