Its all about the ETOPS

Before moving on to another plane spotter post or something new, I thought I'd talk about ETOPS and how it explains the designs of the A340, A330, and B777.

So what is ETOPS?

Strictly speaking, ETOPS stands for "Extended-Range Twin-Engine Operational Performance Standards", but its more commonly said to stand for "Engines Turn Or Passangers Swim". ETOPS is the distance (measured by time) a twin engine aircraft (and airline) is allowed to be from an appropriate emergency diversion field should one engine fail. So for example, an ETOPS-90 rating means that the aircraft is allowed to fly a route that would take it no more than 90 minutes from an appropriate airport with one engine running. There are four levels of ETOPS:

• -75
• -90
• -120/138
• -180/207

Originally, prior to the 1980s (in the U.S. under the FAA) the only rating was just "ETOPS" which meant any operation over 60 minutes from a divert field for twin-engine aircraft. This 60 minute rule comes from the days of piston commercial airliners, whose engines were notoriously unreliable. Just as an interesting side note (for me), ETOPS was originally just EROPS, or Extended Range Operational Performance Standards, which applied to all aircraft. ETOPS wasn't created until much later in the 1980s, when the reliability of engines had reached the point where tri- and quad- engine aircraft did not need to follow EROPS.

How are ETOPS ratings decided?

Quite simply, ETOPS is all about engine failure probabilities (or inflight engine shut-down rate) in twin-engine airliners. The lesser the probably one engine will fail, the higher ETOPS rating it can be awarded, and in turn the remoter it's route can be. The failure rate is the magic statistic because the FAA asks three main questions: What is the likelihood one engine will fail inflight? Can the aircraft reach the desired emergency airport from the rating distance on one engine? What is the likelihood the second engine will fail during the diversion? The FAA evaluates each aircraft type AND airline and determines how far they can safely operate from an airport. The FAA take at least the following into account when giving a rating to an airline and its type:

• Engine Failure Rate/Inflight Shutdown Rate
• Crucial Systems (such as Fuel Metering System and Anti-Ice System) Failure Rates
• Crew Procedures and Training
• Maintenance Procedures and Records

Aircraft manufacturers ensure their desired planes will get the appropriate ratings by using engines that have been proved reliable through testing overseen by the FAA and by having redundant systems. Airlines, on the other hand, focus on crew training and enforcing strict maintenance procedures.

As a side note, when I read "What is the likelihood the second engine will fail during the diversion?" I thought that the chances of a double engine failure must be so small that its not worth considering. But then I realized that the disguised question is, how separate are the systems for each engine? If the first engine failure is due to a bird strike, logically the second engine should have no greater chance of a failure. But if the bird damages a common fuel pump for both engines that causes the fuel pressure in the second engine to drop, then that engine might have trouble staying "lit" for lack of a better work. Thus, the more interdependent the engines are on common systems, the greater the chance that there will be a double engine failure. Modern airliners usually have at least double system redundancy, with the most crucial systems such as the hydraulic and fuel pumps, electrical generators, and FADECs having triple or quadruple redundancy.

Why are ETOPS ratings so important?

Taken from a customer prospective, the first reason is quite obvious: ETOPS helps ensure safe operations on long-distance or remote routes. But the advent of high ETOPS ratings has greatly added to efficiency both in terms of money and time in the airline industry. Often the remoter routes (such as those that cross the oceans far from land and the Arctic circle routes) are shorter than there lower ETOPS rating counterparts. The more common example is the New York City to London route. Prior to ETOPS-90, all twin engine aircraft could not go straight to London or NYC, but instead had to arc close to Newfoundland, Greenland, and Iceland, in order to stay within 75 minutes (since they would be under ETOPS-75) of a diversion field. Instead, airlines would have to fly the more expensive and sometimes oversized (for the route demand) aircraft such as the L-1011 Tristar, DC-10/MD-11, or the classic B747. So since the creation of the ETOPS rating system by the FAA and the resulting efforts by most airlines to meet the standards for each optimized route, ticket prices and travel times have decreased.

Now that I've explained ETOPS ratings, I can move onto the existence of the A340, A330, and B777 and why the B777 was/is such a successful aircraft. But as I was putting my thoughts together to explain it all, I realized that it is more complicated than I thought since the obviousness of the answer to me is due to things I have probably incorrectly assumed are common knowledge. So I've decided to stop this post here so I can think about how I want to explain the A340, A330, and B777 question. If you would rather have a short summary answer and move on to something new, I can do that also. I realize that ETOPS is not exciting to read about, but I suppose its importance in the aviation universe is enough to justify this post... I hope. If you have any questions, just let me know.