Originally Posted by
WhatsaLizad?
The Lottery jackpots for 3 numbers are significantly less than those for 4 or 5 numbers
Don't understand me wrong, I understand what you are trying to say. But you are talking about non-recoverable failures. The B767 had a common cause which is (probably) a result of non-bullet-proof failure analyses (well failure analyses will never be bullet proof). But such discoveries will certainly lead to modifications to aircraft or maintenance changes and hence shouldn't happen anymore.
The Boeing checklists in these cases aim at recovery of systems: they isolate and try to re-establish step by step. Ie, it's a known basic sim-scenario on the B737 to trigger a complete loss through an AC demand system (hydraulic pump), and have the crew walk through the checklists and identify the cause. The reasoning is 3 or even 2 different generators (power generation) on themselves don't fail around exactly the same time, those do require lottery number chances. A user can trigger the failure, but in these cases generators should be recoverable.
I do have to say I started on non-EFIS classic 737's. The "one fails, one overloads" could indeed be a problem because the APU generator did not have the same output as an engine driven generator, and the APU itself was dodgy to start... You also had 30' of battery life (if the battery was new) and if you wanted to start a dodgy APU you lost a couple of minutes already... Meanwhile, the flying pilot was looking at tiny standby dials. At a certain point he would discover the trim is not working, you are on manual trim now. And when you've finally "composed yourself", the dreadfull "tuut tuut tuut" comes on and you have to reach for the oxygen mask. How much time left now? About 20 minutes to land? Then came the EFIS (hey look the captain has good instruments to fly these 20 minutes!).
This sounds like story telling, but I only mention it to point out that - even on battery only - it's not that easy. The captain is flying and pretty much has to do... everything.
Then came the NG... 60 minutes battery? Holy moly... So it is 60 minutes to reach an airport but more importantly... 60 minutes to try to recover something. Because chances are big that one of those 3 generators will be recoverable. Non-recoverable power generation - IS a case of lottery numbers...
But I'll take the NG any day, beats the 30 minute battery classic ;-). Same rules did apply though.