(Sniped by TDR...)
777 and 787 have both a hydraulic pump and an AC generator on the RAT shaft. RAT deploys for triple hydraulic failure or full AC loss.
Originally Posted by
WITCHWAY550
td...... I opened this topic with purpose but my reply needed to be directed to the smartest person on this topic. I am retired. Starting flying when I was 14 and just retired 4 years ago at 67. I flew for Eastern on the 727, A300 and DC-9. My younger brother , Capt B.P. Witcher was hired by United in 1985. The following is relative to my question. It involved my brother.Late on the evening of April 13, 2004, United Flight 854,
Boeing 767-300 service from Buenos Aires, Argentina, to
Miami, Fla., was in cruise flight at FL310 over the jungles
of southern Colombia, South America. Capt. Brian Witcher
and First Officers Donald Arlotta and Ross Windom were
the flight crew that night.
Brian and crew had a total electrical failure in flight. They landed in Bogota 42 minutes after the onset of the issue, most of that time on the main batteries only with intermittent AC/DC power. RAT did not deploy and presumably unavailable to them particularly once the issue was found afterwards by maintenance. Corrosion on a common bracket which grounds both AC/DC to the fuselage.
Were you aware of this event? I learned or was told that the RAT cannot be manually deployed and will not auto deploy if the generators have normal output, which they did in this case.
This was an ETOP aircraft.
Thanks
Billy Witcher
757 and 767 have a hydraulic-only RAT.
There is then a (optional but probably present on ETOPS) DC hydraulically driven generator (HDG) that more-or-less just keeps the batteries topped up.
If the bleed air driven demand pump (ADP, assuming loss of electric pumps) is keeping the centre system pressurised, there is little point in deploying the RAT to also pressurise the system. The HDG will run happily off the ADP's flow.
This is not that dissimilar to the A330/A340 situation except their EMER GEN is AC output.