On April 18, 1983, sector ORY (Orly)-ATH (Athens) in a B707-340C freighter aircraft with registration AP-AWU and call sign, Pakistan Eight Zero Six.
We had to land back at Orly from 50 miles out because Flight Engineer Nadir was unable to control the aircraft pressurization since the panel was a little different. He told me that it was malfunctioning; he couldn’t stop the cabin from climbing. Departure was at 1225Z and return to Orly at 1350Z.
With me that day was co-pilot S.R. Hasan, Flight Engineer Nadir and a flight attendant. On return to Orly, the ground engineers demonstrated to Nadir after pressurizing the aircraft on ground that the system was normal. We departed again at 1700Z, and around the same altitude out of Orly, Nadir gave me another scare by repeating the same story. However, in a little while he was able to manage the system and we continued to Athens without further fuss, arriving at 2015Z.
On April 18, 1985, we were given a B720 with registration AP-ATQ to operate a scheduled domestic passenger flight on sector KHI (Karachi)-FSL (Faisalabad)-KHI. With me was the same copilot, S.R. Hasan, Flight Engineer Iftikhar Moghal and Cadet Flight Engineer Sohail Fazal. Departure time was 0833Z, but we returned back to Karachi at 0928Z from an altitude of 17,000 feet because the aircraft could not be pressurized. The main blower valve (blue light) which automatically closes at a pressure differential of 2.5 psi in the pressurization system, and had to be closed manually due to a system malfunction; it could not be closed, according to Moghal.
As a precaution, we had donned our oxygen masks in the cockpit and to accomplish this task, Moghal, wearing a portable oxygen mask, went below the cockpit via steps into a compartment called the lower 41 which houses the equipment racks for the electronic systems, and where the manual operation to close the main blower was to be conducted. He left the cadet sitting on his panel. On return to his seat, Moghal, rather visibly disturbed dropped the oxygen masks for the passengers as we went through the descent checklist, and while simultaneously starting a descent for 14000 feet.
On arrival at Karachi, the ground engineers were skeptical that the blower valve could not be closed. The dropping of the oxygen masks in the cabin did not go well with them either, and they demonstrated after pressurizing the aircraft how easy it was to close the blower valve manually. However, another B720 aircraft, AP-AXM was provided to complete the flight and this was done without further interruption.
The next day I had to present myself for inquiry at Flight Operations Dept. in the Head Office, where both of us were called. I was asked why the altitude had reached 17,000 feet, and from this I gathered that this was to have been handled much earlier, but I couldn’t leave my station in the aircraft or monitor the Flight Engineer when he visited the lower 41 compartment in the air, and so was let off. And so was he, strangely.
It is rather odd that both these incidents occurred on April 18, two years apart and with the same co-pilot.