Thanks guys! Excellent. I thought the engineers were hitting something but from my seat in GMC it was difficult to see, even with binoculars! They seemed to use the aircraft engineers equivalent of a panel beating hammer.
On the Monarch aicraft starting issue ..The Boeing 720B. I remember that on occasion they were started by an air start compressor that was connected by some sort of trunking to the aircraft belly? I do remember an incident when the ‘trunking’ either ripped or the coupling to the aircraft became detached leaving it snaking around like a demented Python. However, my personal favourite was the spectacular flame from each Proteus as a Bristol Britannia started. Sadly something that we won’t see again.