The US Federal Aviation's rulemaking advisory body has just suggested turning the old extended-range twin-engine operations (ETOPS) rule on its head.
It appears that appropriately equipped modern twins may be allowed to fly almost without restrictions over large oceanic and inhospitable wilderness areas, but many older three- and four-engined aircraft that used to have that privilege would, if the proposal is mandated, be more restricted in what they may do than the new twins. The FAA now has to consider whether to adopt as a notice of proposed rulemaking this report by the Aviation Rulemaking Advisory Committee (ARAC), a body representing industry, regulators and interested organisations.
Acknowledging the technological advances by new twins like the Airbus A330 series and Boeing's 777 in an ETOPS review seems a fair proposition, but their unique limitations compared with aircraft that have all their advantages - plus additional engines and more systems redundancy - still have to be considered.
The proposed big somersault is in the change of attitudes toward existing trijets and quads, like the remaining McDonnell Douglas DC-10-30s, the Boeing MD-11 and 747. The USA used to consider them safe enough to be free of the rule that restricted modern twin-engined aircraft to flying 180min maximum single-engined flying time from usable diversion airfields, but now it does not. There are, understandably, proposed upgrades for cargo hold fire suppression which would mean retrofits for some of the older trijets and quads, which might well be uneconomic. The newer A340, however, complies with all the proposed equipment redundancy and long-period fire suppression conditions so it should not be affected. But it will be, because of the proposed new clause that says having two additional engines should make no difference beyond 180min diversion time. If that is the case, then ARAC is being highly selective in its definition of redundancy, choosing to take account of redundancy provision in all equipment categories except propulsion and electrical power generation, which is a difficult line of argument to follow considering how fundamental they are. An engine on a 777 is no more likely to fail than one on an Airbus A340. But when a failure does take place or a precautionary shut-down is essential, the Airbus crew is left with some propulsive redundancy and therefore operational choices as to whether to continue or divert, whereas the 777 crew has no propulsive redundancy left.
The ARAC report is a carefully argued reversal of US thinking - rather more like a legal document than a regulatory one. The older trijets/quads would be granted a limited grandfather-rights period of six years from the rulemaking date. This is about the time, coincidentally, that most of the US carriers expect to have divested their fleets of those aircraft.
Most of the younger 747s and MD-11s by that time will - if the current distribution of the types has any bearing on the future - be in the hands of non-US carriers. Theoretically, then, they would not be bound by any ARAC-based FAA ruling, but by their own civil aviation authority's future regulation, and US thinking now appears to be unique. The European Joint Aviation Authorities Certification director Yves Morier makes it quite clear that, if the FAA chooses to follow the ARAC line in its rulemaking, there will be a dramatic gap between the ETOPS standards on either side of the Atlantic.
The JAA differentiates between ETOPS, for modern twins, and LROPS (long-range operations) for those trijets and quads that meet all the upgraded back-up and fire protection systems requirements.
In many areas requiring safety hardware improvements, the USA and Europe appear to agree. Where they diverge most dramatically is in the redundancy required for propulsion systems and electrical generation. For an aircraft to fly more than 180min from a usable diversion airfield, the USA is happy with two engines, Europe wants three or four; the USA is happy with three electrical generators, Europe wants four. It is impossible to ignore that soon the product lines of US manufacturers of large civil aircraft will be made up largely of twins, while Europe's Airbus will be producing the A340 series and the A380 - both four-engined jets.
Boeing talks of this as "levelling the playing field" for twins and quads. But rulemaking on operations and certification safety issues is not about levelling a commercial playing field for different kinds of aircraft, it is about ensuring that each category achieves equivalent safety taking into account its own limitations, and that is not the same thing.
Source: Flight International
