B757-200
Confusion; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Human Factors
Just before push; experienced a brief power surge just like those experienced when the groundman pulls the external power cord before having transferred power to the APU. Because we were already on APU power at the time; I thought it was a little strange; and noticed a brief 'Warn Flex' message appear then disappear; but everything seemed to be normal. Taxi and takeoff went normally with the First Officer as pilot flying. At around 700 FT AGL Captain's flight director disappeared. Glanced at First Officer's panel; everything seemed normal; so elected to continue to altitude to sort it out. It is important to note that at no time during the entire flight did any EICAS messages appear. At initial level off; First Officer discovered despite normal indications on his PFD; the autothrottles were not functioning; and VNAV function did not attempt a level off. Quickly determined that all flight instrumentation (attitude; HSI; airspeed; altitude; and VSI) were normal. Continuing to cruise altitude; we determined that most of the automation had failed to include the Captain's flight director; Captain's speed bug; PFD altitude annunciator (the one on the right which repeats what is put into the altitude window); autothrottles; all VNAV functions; and we had a 'No autoland' on the ASA. FMC would not accept any altitude inputs. LNAV indications seemed normal for navigation purposes; and since we had a basic airplane we could safely hand fly on such a short leg; elected to continue rather than returning in the interest of inconveniencing only one set of passengers rather than two. Determined that there is no guidance whatsoever in the QRH for such a situation. In the descent; pilot flying began slowing the airplane; deployed flaps to 5; when we were assigned a visual. We determined that since we couldn't trust the automation; a visual hand flown approach was best; but elected to put the RNAV into the FMC for some reference points. Descending so as to make [the FAF] by 1;600 FT; the aircraft began to accelerate; called out 'watch your speed'; and just as the correction was being made we went co-altitude with the tops of a puffy scattered layer. Mild turbulence/gust associated with cloud tops caused an airspeed excursion and I observed a 5 knot flap overspeed for about 3 seconds (225 KIAS at flaps 5). Rest of the approach; landing and rollout were uneventful. On the ground; maintenance performed all manner of testing and could not determine the cause of the power surge; reset everything; and all appeared to be normal. So they signed off the reset and the flap overspeed inspection; and we boarded passengers. After the jet bridge was pulled; and about to push; we experience another power surge just like the previous one; but with multiple status messages appearing this time. As I was speaking with maintenance on the radio; another power surge occurred. We deplaned the passengers; and maintenance changed out what one of the mechanics referred to as the 'brain box'; and signed off the airplane. Upon direct questioning; however; we determined that the cause was still unidentified; and changing out a component could not definitively be said to have cured the problem. I didn't feel justified in boarding passengers under those circumstances. After a discussion with maintenance and dispatch who was in contact with the Duty Manager; I indicated that I was only willing to board passengers on a revenue flight after a Functional Check Flight was performed. They agreed; and we performed an FCF testing all automation modes which all worked properly. Return flight [was] uneventful. I cannot say whether or not fatigue played a role; but the First Officer and I had both arisen at our respective homes around to make an early sign in that morning. Whether there were some insidious effects (attention span; etc.) as a result later in the day we can only speculate.
B757 Captain experiences a power surge when external power is removed although the APU generator was in use. Once airborne many auto flight anomalies are detected but the short flight is continued to destination. Maintenance can find no faults but resets everything but prior to pushback more power surges occur and the passengers are deplaned for more maintenance and a test flight.