CloudNine From United States of America, joined Apr 2001, 68 posts, RR: 0 Posted (12 years 1 month 3 weeks 6 days 2 hours ago) and read 1584 times:
First I must apologize because I double intered my last 2 topics.I noticed on Airbus's website that they contend,because of ETOPS they'er new 340-500's will be a safer and more economical aircraft to operate over that of the B777's.For an airline with Trans Pacific sevice and ETOPS in mind,what will be the two biggest differences in these two aircraft on U.S.to Asia routes?
PhilB From Ireland, joined May 1999, 2915 posts, RR: 14 Reply 1, posted (12 years 1 month 3 weeks 5 days 22 hours ago) and read 1524 times:
When an engine stops turning on a 777, 200+ souls will be reliant on one engine and one generator taking the whole strain for up to 3 HOURS and the trip to the diversion airfield will be at a slower speed than cruise.
On the A340 when an engine stops turning the 200+ souls will still have a large built in redundancy, have back up equipment still available, will probably only notice a difference if the crew decide to divert and will reach their destination, or diversion airport, with only a small delay.
In the case of other problems such as smoke or fire, the 340 will, again, be faster to the diversion point.
Would you buy a ticket on a 777 to cross the Pacific? Of course you would, twins have proved safe and reliable over long uninhabited stretches for the best part of 20 years now and they can now operate anywhere a quad can (apart from a small piece of the Pacific of the coast of Chile and Peru).
But would you buy a ticket on a 777 if the airline said "there is a remote chance that you and the 200+souls travelling with you might find your journey includes 3 hours of single engine operation"? Think about it
Ambasaid From , joined Dec 1969, posts, RR: Reply 3, posted (12 years 1 month 3 weeks 5 days 15 hours ago) and read 1489 times:
Just to clarify your points, the 777 isnt reliant on one generator following the failure of an engine.
In the case of smoke/fire, there is no requirement to descend, therefore the 777 cruises to its destination at a quicker speed than the A340!
Finally, remember that at least in the twin you have an airport within 3 hours, this airport MUST have suitable weather for a landing during any time that you might land there. You dont have this luxury on a Quad, there is NO requirement for enroute diversion airports!
PhilB From Ireland, joined May 1999, 2915 posts, RR: 14 Reply 4, posted (12 years 1 month 3 weeks 5 days ago) and read 1473 times:
Taking your points backwards, there is no reason for a quad to divert to an airport with one engine out (unless there has been substantial damage to the airframe due, say, to uncontained turbine failure). Take a look at the 180 minute exclusion areas and you will find that there is virtually no difference between areas of operation between a quad and a twin on almost every route around the world, as there was when the 120 minute rule was the maximum.
As to fire, the maximum cruise speed of both the 777 and the A340 is Mach .85 (the 777 long range cruise speed is Mach 0.025 faster than the A340) but experience indicates that the A340 can maintain maximum cruise for longer with less fuel burn than the 777 and the A340 descent profile from altitude is steeper than the 777.
As to the 777 not being reliant on one generator; when an engine is shut down, the associated systems are either shut down (if the cause of the failure hasn't already done it for you) or transferred to be driven by the other engine - but this is done sparingly as you are adding load to a system that has already been robbed of 50% of its power capacity.
Either way, the basic premise remains - an A340 crew would only think about diverting for a one engine shut down if it became necessary due to colateral damage, a 777 crew would HAVE to as soon as the shut down happened.