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Hello Capt Lim,
My question with regard to the Boeing 777.
Today, when Airbus is testing its new version of the A340-600, I am wondering what are the benefits of equipping two or four engine on an aircraft. Both planes are about of the same size and range capability and they are believed to bring about an interesting competition.
(1) Will Boeing be capable of making the B777-200 flying more fuel efficient and therefore fly further as it has only two engines?
(2) Is Airbus A340-600 able to compensate this loss by flying direct routes as no
ETOPS regulations force it to cruise along potential diversion fields instead of the straight path.
(3) Is it also an advantage when one can distribute the requested thrust on four engines?
Chris Jeker
Hi Chris,
Thank you for your questions regarding the Boeing 777 design. Here are thenanswers to your 3 questions:-
(1) Improving the fuel efficiency of the aircraft will require more fuel efficient engines. The Boeing 777 are fitted with either the Rolls Royce, Pratt and Whitney or General Electric engines. Fitting which type of engines on the Boeing 777 will depend on the preference of the individual Airlines.
You will notice that the Boeing 777 does not have winglets like the A340-600 or Boeing 747-400. Someone once asked me whether fitting winglets on the Boeing 777 will make any difference to the efficiency of the wings. I am made to believe that it does not, as the Boeing 777 is the first aircraft to be completely designed by computer. Therefore, the current wing design is the most efficient one in terms of fuel saving.
Remember that even with only two engines as compared to the A340-600 with four, the Boeing 777 engines are larger and produce more thrust each. Further, Boeing has produced the Longer Range B777-200 with a range of 8820 nautical miles as compared to the A340-600 with 7500 nautical miles.
So your question, will Boeing be capable of making B777 more fuel efficient, the answer is yes if more fuel efficient engines are fitted. Currently, from the data that I have, the Longer Range Boeing 777-200 with two engines flies further than the A340-600.
(2) You are right that the A340-600 is not governed by the ETOPS (extended twin-engine operations) Regulations. The Regulations prohibit a twin engine aircraft to operate over a route that contains a point further than 60 minutes flying time from an adequate airport at the selected one-engine-out diversion speed. This is based on a single-engine flying time to an adequate airport. The diversion time may be 90, 120, 180 or 207 minutes.
This diversion time varies depending on the safety records of the particular Airline (many factors taken into account). The maximum diversion time is only used for determining the area of operation and only granted by the individual country's Department of Civil Aviation.
Back to your question. With the advantage of four engines, the A340-600 can certainly fly direct routes as they are not governed by the ETOPS Regulations.
(3) The issue of two versus four engines has its pros and cons. Your view, if I interpret it correctly, that with four engines, you can distribute the thrust when you needed them, is true in the sense that you only lose 25 percent of the take-off power in the event of an engine failure. So you can still distribute 75 percent of the power to the aircraft. In a twin-engine aircraft, you lose 50 percent of the take-off power (which is not necessarily the maximum power). However, Design Regulations required that the remaining single engine must have sufficient power to meet all the requirements that are applicable even to a four engines aircraft that suffers from single or twin engines failures.
Thus, with four engines, whether it is a plus is debatable. Power-wise, it makes no difference. ETOPS, yes, range-wise, no. You also have to consider operation and maintenance costs, noise level, comfort and many other factors before you can decide which is better. Since I fly the Boeing 777-200, my choice is still with two engines.
I hope I have been able to answer your questions satisfactorily. I do not
represent any Manufacturers and my views are my personal ones.
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