One of the more gratifying parts of doing what I do is hearing from so many people who have such an interest in everything to do with airplanes. And I'm constantly amazed at the depth of knowledge folks have, and the smart questions they raise.
For example, here's a thought-provoking note sent to the blog recently:
I have been quite enamored by the engineering story of how 777 was designed and built. It's a great story of innovation, supplier collaboration and the use of technology for practical results.
The 777-200ER is the real deal. I never believed that A380 made much sense - Boeing's vision of interconnecting cities is not only practical but represents the way folks will like to travel.
The only thing that perplexes me about 777 is that it only has 2 engines. Perhaps I'm conservative, but somehow 747's 4 engines gives me comfort that there's a lot more redundancy built-in in case of engine failure. Sure, the stats may show that the probability of such failure is very small, or that 2 engines is statistically as safe as 4. But it's more psychological I guess. Did Boeing conclude that 4 engines would push the cost way up?
C.J. Tan
Thanks for the note, C.J. Here's the short answer: we've been studying this issue a long time, dating back decades. It's something known as ETOPS, or extended twin-engine operations. ETOPS goes back to the days when engines were less reliable and a twin-engine airplane was restricted to flying no more than 60 minutes from a diversionary airport, where it could touch down if a problem arose in-flight. Old-timers like me might even remember when it was called the "60-Minute Rule."
But since we launched the twin-jet Boeing 767 into service on transatlantic routes in the mid-1980s, engines have improved significantly, and twin-jet airplanes operating on ETOPS routes now operate to higher standards of reliability. And ETOPS rules have been increased to as much as three hours or more (in the case of the 777), based on the success of the 767 and 777 families.
The Boeing 767 - the ETOPS pioneer.
We now have a lot of years of data and flight records showing that twin-engine airplanes are more efficient, more economical, and most important, more reliable than four-engine airplanes.
Twin-engine airplanes encounter far fewer diversions and turn-backs than four-engine airplanes. A good example is the fact that the four-engine Airbus A340 has twice as many turn-backs and diversions as the 777. For the passenger, of course, this means that on a twin-engine airplane like the 777 you're less likely to be inconvenienced by departure delays or unscheduled stops.
In terms of the "comfort" or psychological factor you mention, consider that since 1985, airlines around the world have flown almost 4 million ETOPS flights. ETOPS twin-engine operations and airplanes are clearly the most convenient and reliable way for people to fly.
Now, since operating with twin-engines is proven safe and reliable, it only makes sense to take advantage of the increased efficiency they offer. Twin-engine airplanes consume less fuel, weigh less, have fewer emissions, and operate more efficiently than four-engine airplanes.
We figure it amounts to 5% to 9% lower operating costs for airplanes of comparable capacity, range and level of engine technology. And by consuming less fuel, twin-engine airplanes are also friendlier to the environment.
Twin-engine ETOPS flight also benefits the traveler. It allows airlines to offer more direct flights to more destinations with more frequencies, and with fewer connections and delays.
And if it's any further comfort, independent research has shown that three out of four passengers prefer to fly on the 777 than its competitors. Time and data have shown us that twin-engine airplanes are safe, reliable, and efficient. That's why they're here to stay.
If you want to read more about ETOPS flight, you might want to take a look at this article from Boeing Frontiers online from a couple of years back. It's a good overall look at the subject.
Subscribe to this blog's feed