CallmeJB wrote:Cubsrule wrote:It sounds like we are saying the same thing: it’s a trickier question than merely counting the number of redundancies. Look at fly by wire, for instance. Without manual reversion the aircraft need more redundancies.
When it comes to the Hydraulic systems, yes. The additional redundancies to account for the lack of manual reversion is an engineering debate. One may not be better than the other.
When it comes to the electrical system, there is no doubt: the 767 has more backups than the 737.
But, again, the 2000 mile leg simply is not that long! The 737 and A320 are both, now, adequate at handling those legs from the west coast. It's not a walk in the park, but it's within the design capabilities.
At my airline, a west coast to HI leg IS a walk in the park. A more typical route would be East Coast USA to Western Europe, where the 2000 mile overwater leg is only half the journey; that's the bread and butter of what wide body aircraft do.
The longest leg I've operated in the 767 was a ferry flight from TLV straight to MEM... 15+ hours in flight. The 1500 mile oceanic portion was a relatively small part of that total flight. We didn't coast out in Shanwick until we were past the halfway point in the flight, and when we coasted in over Canada there was still four hours of flying left. If we had lost a generator or a hydraulic pump over the Middle East or Europe, we could have continued across the North Atlantic ETOPS 180 or downgraded to ETOPS 120 depending on the exact failure. Compare that to the 737, where any failure in an ETOPS critical system after takeoff will prevent them from crossing the pond.
As has been noted in this thread before, the 767 was not designed with ETOPS in mind... ETOPS didn't exist when the 767 was designed. But the 767 was designed for long, international legs. Can a 737 fly from Europe to South Africa? Maybe, at the limits of its range, it could do it. Can it handle system failures along the way, and continue? No, most component failures will mean that you are landing short of your destination. The 767 was designed to be capable of handling component failures and continuing to the destination. This is a design requirement when operating to far flung destinations over third-world regions.
The 737 is capable of the relatively easy West Coast USA to Hawaii USA ETOPS route. Is it one of the longest ETOPS overwater legs out there? Yes it is. But you see, that simplifies things: any component failure means a diversion to one end or the other. Either way you are in a populous and advanced country.
The less-easy decisions occur over part of the Middle East, Central Asia, and Africa. Do you divert to Libya, Chad, or continue to your destination of Lagos? Sure, you have the performance to fly single-engine all the way to Lagos, but how do you justify overflying N'Djamena? You can't, you must land. And with choices like that, I'd rather have no choice at all... that's why the Hawaii leg is easy.
-Current 767 Captain (repeated only because somebody questioned it upthread)
Well folks, you heard it all from a real professional.