The LP cock
Can't remember why I went to LHR that day. My base was LGW, flying Daks and Herons. For whatever reason, on my day off, I had to drive to Heathrow. Coming in from the Hounslow direction, I saw a growing column of black smoke rising from the middle of the airfield; too much for a practice by the Airport Fire Service.
Later, I learned that the crew had done a great job doing 5/8 of a left-hand circuit and landing north-eastwards on Rwy 05R, having taken off to the west on 28R. In due course, it was said that the one mistake was that they had failed to close the LP-cock (low-pressure fuel valve) of the engine that had caught fire. As a copilot with no jet experience at that time, this meant little to me.
Apparently, though, the LP fuel valve was at the beginning of the fuel line from the fuel tank to the engine. It was closed by pulling the fire handle, prior to firing the first of 2 fire extinguishers. At the other end of the pipe, at the engine itself, was the HP-cock (high-pressure fuel valve). The crew had successfully closed this when they shut the engine down, using the same lever that is used on a normal shut down.
When the burning engine fell away, however, there would have been nothing to stop fuel pouring out of the severed fuel pipe at the top of what remained of the engine pylon.
3 years later, I converted to the BAC/Vickers VC10, which has slightly more powerful versions of the Conway engine than Whisky-Echo had. The flight-engineer’s fuel panel (designed circa 1963) was/is logically laid out, like a schematic diagram, with switches and indicators showing the positions of the various valves; including the LP valve for each engine. During and after a fire drill, there could be little doubt what was the position of the relevant LP valve.
After another 4 years (1975), I went on the Boeing 707-320C (not BOAC), with Pratt & Whitney JT3D turbofans. But I doubt the F/E’s fuel panel was much different from Whisky-Echo’s, even though ours were newer aeroplanes − also built well after our VC10s. When I saw the indication system for the LP valve, I was dismayed. The only indicator was a dim blue light. When the valve was open, the light was off; when the valve was closed, the light was also off (yes, this is not a typo).
The only indication of a change in the position of the valve was that the blue light came on WHILE THE VALVE WAS IN TRANSIT. So, if the flight-engineer was distracted for the few moments while the valve was in transit, there was no way of satisfying himself that the valve had run shut. And if the fire handle had not been pulled properly, there was nothing on his panel to warn him (and the captain, who can also see the flight-engineer’s panel) that something had not been done; that needed to be done.
Round about 1976, our B707s started to be modified; to improve the LP valve position indication…