Aircraft Cabin Air & Water Contamination/Quality – An Aircraft Systems Engineering Perspective

Abstract

Air conditioning in jet aircraft depends today on bleed air from the engines or APU (apart from the B787). Engine oil with harmful anti wear additives can get into the cabin air. This can be a risk to passengers and crew. The question about "aircraft cabin air contamination" can be related to "aircraft potable water contamination". Aircraft water contamination can in theory be due to a potable water pressurization system with bleed air. Findings are that also the potable water on board can be contaminated from engine oil. It depends on the aircraft system architecture. Examples are given: Potable water contamination from engine oil via bleed air is possible on Airbus A320, A340, (not on the A380) and on Boeing 737, to name a few. Hydraulic reservoirs are connected via bleed lines with the potable water tanks. Pressurized air is in free contact with the hydraulic fluid surface. But, in flight, hydraulic fluid would need to flow upstream and opposite sense through two check valves to get into the bleed line (A320). This is not plausible. On the ground, however, contaminated air with remaining pressure in the reservoir (about 3.5 bar) could flow downstream – but only if check valves allow for wrong flow direction. This is unlikely. This seems to be the scientific way forward: Look for oil contamination in all rotating machinery: engine, APU, air cycle machine (ACM), electrical compressor (B787 has air bearings!). Look for all possible paths on which oil can get in contact with people on board. Today most engine oil contains harmful substances. As long as this is the case it has nothing to do in the aircraft when only the slightest chance exist these substances get in contact with people (via air, water, …). Take a systems engineering view: Think in system boundaries. Argue as simple as possible!