If you look at the film at 0.17 you will see an airman pick up an access panel cover off the ground and fit it underneath the plane. I guess that this panel was left off during engine start to allow his colleague to come with his fire extinguisher if necessary.
I hope someone on this thread can confirm...
Spot on; being a fairy rather than a sooty, the precise details of what lived inside that panel were mysterious, but that was where an Avpin explosion would occur if it happened, and where to squirt the CO2. Once both Sapphires were spinning up, one of us ( + 1 at night to hold a torch) dived underneath to secure 22 Dzus fasteners. Earlier marks had cartridge start, producing great clouds of black smoke.