Safety Investigation Report 2018:1 Factual Information/1.6/1.6.8 Aircraft Systems/11
SAFETY INVESTIGATION REPORT MH370 (9M-MRO)
11) Oxygen Systems
- a) Flight Crew Oxygen System
The flight crew oxygen system provides oxygen to the flight crew for emergencies and other procedures which make its use necessary. The oxygen is supplied by two cylinders located in the left side of the main equipment centre. Each cylinder is made of composite material and holds 115 cubic feet (3,256 litres) of oxygen at 1,850 psi. The oxygen is supplied, through regulators, to four oxygen masks in the cockpit, one each for the Captain, the First Officer, the First Observer and the Second Observer. The mask has a dilution control which is normally set at ‘Normal’ position. In this position the oxygen is diluted with ambient air according to the pressure altitude in the cockpit. It can also be selected to ‘100%’, in which case 100% oxygen will be supplied. Table 1.6E (below) shows the expected duration of oxygen supply from the two cylinders with the dilution control in ‘Normal’ position.
AIRCRAFT ALTITUDE: 36,000 ft Cabin Altitude: 8,000 ft. Cabin Altitude: 36,000 ft. No. of
Crew
MembersExpected
Duration
(hour)No. of
Crew
MembersExpected
Duration
(hour)1 42 1 27 2 21 2 13 3 14 3 9 4 10.5 4 6.5 Table 1.6E - Expected Duration of Crew Oxygen
Aircraft altitude is assumed to be 36,000 ft. A cabin altitude of 8,000 ft. would indicate a normally pressurised cabin and a cabin altitude of 36,000 ft. would indicate an unpressurised cabin. At this cabin altitude of 36,000 ft, 100% oxygen will be supplied even with the dilution control in the ‘Normal’ position.
- b) Passenger Oxygen System
The passenger oxygen system is supplied by separate and individual chemical oxygen generators. The oxygen system provides oxygen to:
- passenger seats
- attendant stations
- lower crew rest compartment
- lavatory service units
The passenger oxygen masks and chemical oxygen generators are located in passenger service units (PSUs). A door with an electrically operated latch keeps the masks in a box until the oxygen deployment circuit operates. The deployment circuit operates, and the masks automatically drop from the PSUs if cabin altitude exceeds approximately 13,500 feet. The passenger masks can be manually deployed from the cockpit by pushing the overhead panel PASSENGER OXYGEN switch to the ON position. Oxygen flows from a PSU generator when any mask hanging from that PSU is pulled. Oxygen is available for approximately 22 minutes. The electrical power to the latch is supplied through a circuit breaker located in the Main Equipment Centre. It is not possible to deactivate automatic deployment of the masks from the cockpit.
- c) Portable Oxygen
Portable oxygen cylinder lets the flight attendants move in the aircraft when oxygen is in use. It is also a gaseous oxygen supply for medical emergencies. The bottle is fitted with disposable mask. 15 cylinders are located throughout the passenger cabin. Each cylinder is of 11 cubic ft (310 litres) capacity. The flow of oxygen can be controlled by an ‘Off-On’ knob which can be rotated to control the flow from 0 to 20 litres per minute. Therefore, the minimum time for the portable oxygen supply from full is 15.5 minutes.