https://www.skybrary.aero/index.php/...066f-276530305
This latest article in the SKYbrary website about the Helios Airline 737 that crashed in 2005 when the crew lost consciousness due lack of oxygen, is worth revisiting. Except for a stroke of sheer good luck, a similar fate could have happened to the crew of a RAAF HS 748. Read on:
The HS 748 crewed by two pilots and a navigator, was en route Rockhampton to Canberra having dropped a VIP at Rockhampton. The Commanding Officer of the squadron was PF under the supervision of the unit QFI (Centaurus) who acted as co-pilot. Soon after takeoff, the QFI adjourned to the cabin leaving the PF and navigator up front. The weather was fine. The aircraft planned cruise altitude was 15,000 feet.
Soon after the aircraft reached cruise altitude, the QFI experienced symptoms of hypoxia. As he explained later, these were green spots in front of his eyes and dizziness. He remembered these symptoms from his aviation medicine course 15 years earlier. That course involved training at the RAAF School of Aviation Medicine at Point Cook in a Hyperbaric Chamber to simulate the effects of high altitude on the human body, especially hypoxia (low oxygen).
He immediately returned to the cockpit and found the navigator slumped over his desk and the Commanding Officer singing loudly like a drunk. A glance at the pressurisation instruments revealed the aircraft was unpressurised and had been since takeoff.
The QFI then saw why. The pressurisation out-flow valve in the HS 748 was controlled by a manually operated lever on the co-pilot's side of the cockpit. It was normal procedure to have the out-flow valve open on the ground and for take off and for the co-pilot to close the outflow valve as part of the after take off checklist. Thereafter pressurisation was maintained automatically.
For some reason the QFI had forgotten to close the out-flow valve after take off and missed the item during the after take off checklist. The CO being new to type missed the item as well.
It was indeed fortunate the QFI recognised the symptoms of hypoxia before it was too late. Clearly the flight safety value of the RAAF hypoxia aviation medicine course proved inestimable. In 2017 it a pity that such a course is not available to civilian crews