Recent heat anomalies up to 12C above ‘normal’

A warming planet poses issues for airlines that many players in the flying game might see as less pressing than aggressive competition, or the struggle to get on top of airport handling or navigational fees, or excessive or misguided regulations.

But this week heat grounded some regional jet operations in heatwave affected airports in the US, in an indication of what will inevitably happen where heat waves become more powerful and frequent than aircraft designers anticipated and begin to have increased operational consequences for larger capacity jets.

It’s technically a more complicated set of issues than set out in most general media reporting, although this New York Times report sets a far higher standard than the pack. (Apart from using the British colonial temperature scale, in some sort of obsequious historical throwback you can fix by just keeping a tab open for degrees F to C conversions.)

It might be helpful to try and reduce these issues to lay terms, at the risk of course of not being strictly or exhaustively accurate in the fine details.

In fact the challenges posed to big jets are already being taken very seriously by Boeing and its GE engine partner in the 777-X program because the overwhelmingly larger part of the orders for this family come from the Middle East or ME3, Emirates, Etihad and Qatar Airways, who all have global hubs that already fit into the ‘red hot’ category. (As well as being prone to fine dust concentrations that make engine washing and contamination control incredibly important to keeping their fleets reliable.)

The hotter the field temperature is the more the atmosphere ingested by jet engines expands, meaning the distance between molecules of oxygen increase, lowering the amount of energy an engine can generate by burning oxygen as it powers an aircraft toward takeoff speed. Hotter, lighter air mass also reduces lift.

That reduction in available power per unit volume of air means the jet takes longer, and has to therefore go further to reach a speed where it can generate enough lift to leave the ground and do so at a safe gradient capable of missing inconvenient obstacles like trees, buildings and terrain beyond the end of the runway.

It means that in some circumstances, the aircraft cannot conform with the safety requirements of a full load, which can be the case even on a ordinary day at airports like Wellington in New Zealand, with a fairly short runway anyhow.

If the jet has only two engines, which is true of most airliners these days, the rules require it to be able to take off safely after one engine fails at a speed which is too fast for it to safely stop before hitting the fence at the far end. “Safely” is defined as being able to climb above a certain height at a specified distance, and for the aircraft to have demonstrated during its certification phase that it remains controllable even under the provocation of crosswinds of a certain strength and so forth.

Slamming on the brakes isn’t a safe option if, as if often the case, the total weight of the jet is higher than the minimum weight at which it can safely land. Landings impose much higher forces on undercarriages than takeoffs. Get an aborted takeoff ‘wrong’ and the heat load in the wheels of the jet can exceed the point at which fusible plugs will deflate the tyres, likely creating a fire more than capable of igniting the full fuel tanks, which will rupture if they gut themselves on a ‘fence’ or ground equipment or beacons and so forth. All sorts of things can go wrong in a split second in a botched aborted takeoff, so the standard operating procedure above a certain speed is to continue the takeoff, ‘limp’ into the air, and loiter, perhaps assisted by a fuel dump mechanism, until the weight of the jet falls to a safe level for a landing, or even just an acceptable ‘overweight’ landing, which will require a subsequent detail inspection for airframe deformations and any repairs resulting from them.

But, big but, if the jet has three or four engines, the safety rules are less prescriptive, in that losing one engine doesn’t have as dire an effect on the aircraft’s ability to climb away from the airport, and the calculations for permissible loads in unusually hot conditions may allow it to avoid a payload penalty if taking off at what might even pass for a heat wave in Dubai rather than a more ‘normal’ field temperature for that part of the world.

A380s can take off in extreme heat conditions at Dubai without the same payload penalties as 777s, or A330s, because getting into trouble with three out of four engines working is a lot less problematical than dragging a dead engine with a much larger diameter into the air with only one engine working.

OK, engine failures on takeoff are rare, but not unknown. The incredible safety performance of modern jets is build on the foundation of insisting on certification standards that address risks that could otherwise result in massive casualties. Besides, no one has yet worked out how to design a viable giant twin engine jet airliner that could take up to 840 passengers, which is what you’d get inside an A380 if an airline tried to pack one as densely as some operators do their A330s, and 787s and 777s.

(One ends up with engine diameters so wide that the outer sections of the fan blades are rotating much faster than the speed of sound, stuffing up their efficiency by having to fight excessive drag.)

The nearest attempt to do this is the forthcoming 777-X, and the ME3 made it very clear to Boeing and GE that their purchase of the type depended on achieving new standards of extreme hot condition performances even though this impending big twin wide body will not have as much potential capacity as an A380.

In the New York Times article the much respected US analyst Bob Mann is quoted thus:

Robert Mann, the president of airline industry analysis firm R. W. Mann & Company, said that although airlines were working to become more efficient now, they were not doing much to prepare for the longer-term effects of climate change. “In a world where they’re focused on near-term issues, the glacial rate of environmental change is not within their fleet-planning horizon,” he said.

Airports are going to experience more heat waves. Even if the mean hot season temperatures average a rise of only one degree C or less compared to now, the distribution of days when the variation is 5C or 8C or even higher than that will become a huge nuisance for airlines and travellers.

Where it is physically possible, airports will come under pressure to extend runway lengths to accommodate weeks in which extreme heat would otherwise curtail the dispatch of fully loaded jets, or even prevent some departures.

Travellers have plenty of reasons now to get hot under the collar about the deliberate degradation of cabin amenity in all classes of carriage as toilets, seat pitch and cushion width are cut back because it makes short term performance metrics (if the extra capacity is sold) look good.

Add to this the self-inflicted stupidity of ignoring the long standing need to curb fossil carbon releasing sources of energy, and the shambles that is mass air transport today is going to become even more discouraging.

(Visited 20 times, 1 visits today)