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> The airlines stopped pumping exhaust into passenger compartments for a few years This is way off the mark. All airliners except for the Boeing 787 [0] press
by jhugo 3y ago
> The airlines stopped pumping exhaust into passenger compartments for a few years
This is way off the mark.
All airliners except for the Boeing 787 [0] pressurise the cabin with bleed air. This is not "exhaust"; it's pressurised air extracted upstream from the combustion stage. There are certain situations where the engine may ingest its own exhaust, or the exhaust of an aircraft in front, or there may be an internal leak in the bleed system. All of these are unintended contamination of the bleed air, not a normal mode of operation. In addition, the compressors ahead of the bleed valves must be lubricated and it is possible for this lubricant to get into the air stream if maintenance (including cleaning) is not carried out properly.
There was no period of time where airlines stopped pressurising the cabin with bleed air. It is the only source available on all airliners except the Boeing 787, and pressurisation is not optional.
[0] The Boeing 787 uses electric compressors to provide cabin air. This avoids some of the risks (leaks inside the engine, for example), but does nothing to avoid others (ingestion of exhaust from the same aircraft in certain wind conditions or from the aircraft in front when taxiing, or lubricants from the compressors getting into the air stream). The compressors are located in the wing-to-body fairing so the possibility to ingest external contaminants is quite similar to in traditional bleed air systems. The most noticeable difference on the Boeing 787 is the higher cabin pressure (lower cabin altitude) and higher humidity, both of which are made possible by structural improvements including the use of composites. Similar improvements (lower cabin altitude and higher humidity) are also present on e.g. the Airbus A350 and A380, which nonetheless — like all other airliners except the 787 — use traditional bleed air for pressurisation.
- vinay_ys 3y agoOil fumes in passenger cabin air is a more common occurrence than everyone likes or wants to believe. I have personally experienced a very bad case of this once. Here's a pretty good paper surveying the root-causes for this issue – https://www.scirp.org/pdf/eng_2018041917372308.pdf https://www.scirp.org/pdf/eng_2018041917372308.pdf
- jhugo 3y agoI agree with you that it's common, and it should get more attention than it does. My parent post is discussing the causes, which do not involve "airlines pumping exhaust into the cabin", and refuting the incorrect idea that they stopped using bleed air "for a few years". For those interested, further reading: * https://en.wikipedia.org/wiki/Fume_event https://en.wikipedia.org/wiki/Fume_event * Search https://avherald.com https://avherald.com for "fume" * https://www.aircraftcabinair.com https://www.aircraftcabinair.com
- hedora 3y agoI never mentioned bleed air, and trying to distinguish between oil fumes generated from the engines and engine exhaust is pedantic, at best.
- jhugo 3y agoBleed air is (on any airliner except 787) what you are breathing in the cabin whenever the doors are closed and ground AC equipment is removed, so your post was implicitly about bleed air. It’s the air that is “pumped into the cabin”. Exhaust and oil fumes both get into cabin air through non-normal situations. They’re not “pumped in by airlines”, and suggesting that they are (or that they stopped for a while and then started again thinking nobody would notice) is sensationalist and incorrect.
- hedora 3y agoThere was a period of time when airlines stopped pressurizing cabins with bleed air while the planes were at the gate and the engines were running. That's exactly the circumstance where the vents upstream of the jet engines are able to pull in the jet exhaust. Every flight I've been on post-pandemic has pulled exhaust fumes into the cabin while waiting at the gate.
- jhugo 3y agoThe decision of which of the two options (APU/engine bleed versus ground equipment) to use to condition the cabin air at the gate has nothing to do with avoiding fumes. Some airports provide the equipment, some don’t, sometimes it’s not available. By the time engines are being started, ground AC equipment will generally have been disconnected and air will be supplied by bleed from the APU or an engine that was already started. The patterns of whether and when ground AC is used haven’t really changed industry-wide at any recent time, and certainly not around the pandemic, so I don’t know where the idea of this “period of time” comes from. Maybe your travel patterns changed, or the ground AC equipment availability/policies changed at your frequently-visited airports. Or maybe the aircraft you are flying on were parked during the pandemic and then the reactivation maintenance (esp. engine washes) was not thorough enough, causing fumes at startup.