B737 cases offer some lessons regarding
RELAY-to- Bus faults.
If you are fascinated by various electrical failure-interactions, you’ll enjoy reading the
report from Danish AIB [HCLJ], re’ a B737 failure of a RELAY to the Battery Bus
(this is an 18-page pdf with photographs of failed relay): the file http://www.aaiu.ie/upload/general/3582-0.pdf“... The crew were not aware that they could reestablish normal functions and indications by switching STANDBY POWER (P5-5) to the BAT position , as the relevant manuals and checklists for the aircraft did not contain procedures concerning this problem....”
“... Furthermore Boeing explains that these incorrect and lacking indications will vary depending on the specific type of extra equipment installed ...
“... Boeing concludes its ... Bulletin by writing:
Boeing has no technical objection to an airline incorporating a loss of Battery Bus procedure in their Operations Manual. However, since there are so many different electrical configurations throughout the 737 fleet, Boeing is unable to publish a generic procedure in the Boeing Operations Manual which will work for all 737-300/400/500 airplanes.
EDIT -- Here's another B737 case:
AAIB Bulletin: 4/2006 G-EZYN EW/A2005/03/02
... Boeing 737-33V, G-EZYN
... 22 March 2005 at 1050 hrs
"... from Nice to Luton ... experienced progressive abnormal annunciator indications.... there were no procedures in the ... [QRH] ... a failure of a contact post ... the R1 relay ... power had been lost from this Busbar in flight.... no drills published for such a failure ... many different configurations of the electrical system in the Boeing 737-300/400/500 fleet have made it difficult for the manufacturer to produce a generic procedure for this failure, although they have provided information to enable operators to write a procedure for their own aircraft...."
These odd electrical mishaps highlight a manufacturer’s annunciation philosophy, and the operator’s associated checklist philosophy. If the aircraft model includes an EXPLICIT “alert” [eg, an annunciator or EICAS message for specific fault], then the QRH will include a crew response.
?? B757 “
MAIN BAT DISCH” message/light ???
[Reviewing discussion in slots # 19 through #29 points up some details.]
IweinVanCaelenberg, in slot #116, you showed a crew’s QRH response to the B757’s “
STANDBY BUS OFF” message. Once you switched the STBY POWER selector to “BAT”, wouldn’t you expect [???]:
-- the Standby Bus to be repowered, and thus the message (Standby Bus Off) to extinguish;
-- and then you’ld expect the “MAIN BAT DISCH” message to appear [???] sending you to that procedure.
The NTSB’s Preliminary report does NOT mention anything about any MAIN BAT DISCH message/light, but the Board’s Preliminary report does mention that lastly the “...flightcrew then reviewed the MAIN BATTERY CHARGER procedure referenced in the QRH....”
It could be that this victim-crew followed their QRH’s printed procedures to the letter.
It may prove ironic that AA had initiated an MD80 modification to add a “BATTERY CHARGER” annunciator (Overhead Annunciator Panel) as just such an
explicit alert.