Hello opsjockey,
I just started flying ETOPS. Besides extensive material that I received from the company I also used the internet to prepare for this new challenge. ETOPS is at its most restrictive during the planning phase of the flight.
I think we use the JAR limits. First off the potential ETOPS airports have to meet adequacy requirements (pretty important that you have a good grasp of Adequacy versus Suitable when it comes to airports) for the aircraft concerned. As far as weather goes we look at potential ETOPS airports for suitability by adding 400 feet and 1500 meters to the most restrictive limits excluding CAT II/III. If the airport has two runways you can reduce these additions to 200 feet and 800 meters. There are exceptions like State minima that are used for Alternate airports in the USA and Canada (basically 600 feet / 3200 meters for precision approaches and 800 feet / 3200 meters for non-precision approaches). Also wind is taken into consideration and has to be within operating limits (including gusts). These weather conditions have to be met for the entire time that the airport can potentially be used for diversion. The time window opens at the earliest possible arrival time (basically the fastest way you can get there from the ETOPS entry point), and closes at the latest possible arrival time (this is basically a return from the farthest point from the airport flying at 10,000 feet).
The circle size expressed in minutes (120, 180, etc) is translated into a distance by the application that your company has made as to the one-engine cruise speed. This is part of your ETOPS approval from your regulatory agency. My company has elected to use 310 Knot Indicated Airspeed (This translates to a 420 knots groundspeed in no wind conditions). So our 120 minute circle is 840 nautical miles, our 180 minute circle is 1260 nautical miles. This is for the Boeing 767-300ER.
For fuel, three scenarios are compared to each other and you have to meet the fuel requirements for the most restrictive one. The three scenarios for diversion are 1) Engine-failure. 2) Decompression. 3) Decompression and simultaneous engine failure. Usually scenario 2 is the most fuel intensive.
Lastly the MEL plays a much larger role in the flight planning. Items that would not have much of an effect on a normal flight might make ETOPS impossible. As an example a flight can be made non-ETOPS with an unserviceable APU, while ETOPS will not be possible with that same fault. The MEL applies in our case until the application of take-off power.
There are a number of things that have to be met by your organization. Maintenance procedures are different for ETOPS aircraft. Special monitoring programs have to be in place. And many things outside of my expertise are involved.
I use the following internet site to take a look at things before I undertake an ETOPS flights. Lets you play around with different things, and gives a brief explanation of some of the subjects involved.
http://gc.kls2.com/faq.html#$locations .
I don’t claim to be an ETOPS expert, and some of the things that I mentioned are more complicated than I state. I hope you can understand the spirit in which this information is given.
Regards, O.