When performing any engine runs always .... chock the wheels.
I've got good reason for knowing that's wrong. Some time ago in the A340 discussion I said that chocks shouldn't touch the wheels but be set ahead of them by about a foot. Welllll ...... The wrath of the Eng and Tech city fathers came down on my head - until some kind soul posted the passage from the 747-400 AMM. Bingo.
