An appeal from Boeing has put extended range twin-engined operations (ETOPS) in the headlines again. It does not take much to regenerate heated ETOPS debate among those within the airline industry or those outside.
For some time now Boeing, and Pacific route operators of its 777, have been pressing for a 15% extension to its existing clearance to fly up to 180min from the nearest usable diversion airfield. This extension of 180min to 207min would get rid of a relatively small, but annoying, geographical triangle in the mid-Pacific, which twin-engined commercial airliners have to avoid.
Boeing advances the argument that the traditional system of adding 30min or 60min increments to existing limits as technology and proven engine reliability advances is flawed. That argument is clearly true in the sense that the figures are arbitrary, but disingenuous because evolutionary progression has to have a timescale of some kind.
Boeing is clearly ready, however, to abandon the idea of evolutionary progression from the 180min point onward, arguing that demonstrated twin-engine reliability, given the additional systems redundancy already required of ETOPS aircraft, is now good enough to enable the ETOPS concept to be consigned to the history books. Boeing ETOPS vice-president Chet Ekstrand explains: "We built the 777 to have the reliability and redundancy for unlimited ETOPS." No-one would doubt Ekstrand's sincerity or Boeing's aims for quality in its products and their design. Striving for perfection, and its rewards, in a product with an affordable price tag, however, has been subjected to scrutiny before and will certainly be this time, too.
ETOPS has been evolutionary so far for good reasons. From its origins in the days of big piston engines, when shutting down one out of four engines on a transatlantic crossing was a routine occurrence, ETOPS progressed massively as the world became gradually more confident of the jet engine's reliability and power reserves. By the early 1980s, when the 767 and the Airbus Industrie A310 arrived on the scene, the world was ready to regauge fundamentally what was prudent. The regulatory agencies did their assessments, added crew training and systems redundancy requirements like auxiliary power units which can be started and run in-flight, then ruled for a stepped advance from 90min to 120min, and eventually to 180min.
Boeing proposed another new concept during the development of its 777. This was to clear the aircraft for 180min ETOPS at service entry. The US Federal Aviation Administration, at first reluctant, worked with Boeing through an unusually extensive test programme, and acquiesced.
Boeing's new proposal should be examined as a potentially viable idea in the light of the success of worldwide ETOPS over the past 15 years. It should, however, be subject to merciless scrutiny by the regulators, simply on the grounds that issues other than reliability alone come into play when time and distance to a point of safety while over an ocean or wilderness become ever greater. One such issue is search and rescue. The industry is obliged, even if the proposal is an optimistic one, to assume that everyone on board may survive the ditching or an emergency landing. They must, therefore, have a reasonable hope of rescue.
Of course - and this is the basis for Boeing's argument - three- and four-engined aeroplanes are already cleared to ignore the realistic search and rescue requirement. Perhaps, then, as longer aircraft ranges and the spread of world prosperity open up routes over ever more vast areas of wilderness, the search and rescue issue should determine the routes aircraft of any type may fly. Meanwhile, there is no statistical evidence - yet - that modern twin-engined aircraft are any less safe than modern four-engined ones. Simple mathematics, however, dictate that, following an engine shutdown, the twin is left with one engine and the four-jet with three.
The fact that this subject continually excites such emotion is not a point that should be lost on those who have to make decisions. Science and statistics are an essential part of ETOPS extension decisions, but perceptions and values must be heard too. Just because you can do something it does not mean that you should.
Source: Flight International
