Despite attempts to harmonise, the US FAA and European JAA are nearing different final proposals about how ETOPS could advance
The regulatory guidelines known since 1985 as ETOPS (extended-range twin-engine operations) are about to have their boundaries pushed outward again. There is nothing new about that - boundaries have been advancing ever since 1953, when the US Federal Aviation Administration took the first decision about how far into the Caribbean a twin-engined, piston-powered airliner could fly safely, because at that time single-engine performance on twins was marginal and engine failure common.
At that time, the allowable single-engine flying time from the nearest diversion was set at 60min, and until 1963 the FAA still restricted tri-jets to one hour diversion time. But ETOPS as a term was not in operational use until 1 February 1985, when a Trans World Airlines Boeing 767 flew from Boston to Paris under the new rules. A great deal of experience has been gained since then. The 60min rule expanded to 90min, then 120min, and gradually pushed upward as in-service experience demonstrated ever-improving engine reliability levels, with never an incident of both engines failing for unrelated reasons.
That remains true today. Now, with the guidelines at a maximum of 180min - and special dispensation to extend that to 207min in approved cases - the American-led Aviation Rulemaking Advisory Committee (ARAC) to the US Federal Aviation Administration has effectively recommended an extension to 240min. All the signs are that the FAA will accept ARAC advice when it publishes a notice of proposed rulemaking in August.
Certainly, a look at the reliability statistics of the latest turbofans should make a pilot in a one engine inoperative (OEI) situation in a twin-engined aircraft feel confident. According to Boeing there have been only two 777 OEI diversions in the ETOPS phase of flight - that is more than 60min and less than 180min away from a usable diversion airfield. Both diverted without further incident, and only one pushed the 180min guideline to the limit (United Airlines' diversion to Kona, Hawaii, on 17 March). It should not matter how long a successful OEI diversion takes, provided it works - and statistics say it almost certainly will.
But it is a fact that the pilot of an OEI twin in the ETOPS sector of a night flight over an ocean or a mountainous region knows he or she has no power unit redundancy left. An increase in OEI time will prolong the lonely feeling - that acute straining of the ears for any change in engine tone - however sensitive the crew know the engine and systems monitoring equipment is.
Surely, however, with engine reliability statistics as impressive as they are, gut feelings should take second place to logic. So what is the logic, in its fundamental form? In favour of ETOPS extension is the historical fact that the allowable flying time to diversion airports has been extended in the light of experience - of demonstrated improvements in engine reliability. So far, the step-by-step progress has not been proved foolhardy. Since this is so, and additional benign experience has been gathered, it is surely reasonable to push the limits further. That is how mankind has always taken advantage of advances in technology. After all, the 180min figure is a guideline, not a regulation - even if it is treated like one. And the figure is arbitrary, not absolute.
Logic applied for the opposite case is that the further ETOPS routes are permitted to stray from usable diversion airfields, the longer the exposure to a situation in which there is no redundancy left, and risk - however low - is directly proportional to the time spent in the OEI state. The decision to depart from the philosophy of multiple redundancy in a safety-critical component, especially in the case of polar or other flights in hostile environments, runs counter to a basic aviation tenet.
What it all boils down to is that there is a tenable argument for ETOPS extension and a tenable argument against. The differences in the cases advanced by the FAA and the European Joint Aviation Authorities show this to be true. Perhaps there is a compromise, however. Boeing believes the FAA NPRM may recommend that pilots are given the discretion to extend the limits. For example, in the OEI case in a remote area with conditions at diversions marginal, pilots could decide whether it is safer to continue to 240min ETOPS limits - or more - than to attempt diversion.
But logic has not yet been exhausted. There is another decision available to airlines for routes over remote regions - to use a modern type that provides multiple engine as well as systems redundancy. Then the other complex decisions become irrelevant.
Source: Flight International
