Remember that ad the US Airline Pilots Association (USAPA) took out in USA Today claiming that US Airways was unsafe? There was a specific flight used as an example and that may be coming back to bite the union. According to a letter sent from the company’s flight ops group to the captain, the airplane was found to be working just fine. Hmm. This is like a soap opera.
According to USAPA’s website, here’s what happened that day:
- When
pushing back from the gate, the auxiliary power unit (a backup source of electrical power) and the Hot Battery Bus (a critical source of primary electrical power) both failed – in other words, the plane had no electrical power and no radio communications. None.
- After opening a window to verbally call down to the ground crew (the Captain’s only option), US Airways maintenance was able to restart the power unit, but offered no explanation as to why it failed or any reasonable assurance that it wouldn’t fail again.
So we have a couple issues here. US Airways did a thorough review to see what happened. According to the letter from the US Airways VP of Flight Ops that I’ve obtained, the airline tried to meet with the captain in person to discuss the review but she was unwilling. So they put the results in writing to her.
On the issue of the APU failing, no problem was ever found. The APU (auxiliary power unit) is like a mini-engine which provides power when the engines aren’t running. This is actually used to start the engines on the ground, but it’s not necessarily required for flight. If you’ve ever seen an engine started while you’re at the gate with a big generator nearby, then that’s probably a case where the engines needed an external start because the APU wasn’t working.
Back to this incident, the first entry in the logbook from the captain said “APU failed at gate, unable to restart.” According to US Airways, the mechanics did a test that found no fault with the APU and then proceeded to restart it at the gate without any trouble at all. The captain said she wouldn’t accept the aircraft unless the APU was fixed, but since the mechanics couldn’t actually find any problems that needed fixing, they deferred the issue as permitted by the maintenance program.
That was followed by a second entry from the captain saying:
After APU Auto Shutdown on gate with no external power connected, battery power lasted 3-4 minutes. Unable to restart APU or communicate on VHF [radio] #1.
So the APU failed and wouldn’t restart. US Airways pulled the Electronic Control Box (ECB), which the airline describes as the “brains of the APU.” The ECB records any abnormal events to help with maintenance. So the airline sent the ECB to Diehl Aerospace, which is described as “the repair subcontractor for Honeywell (the manufacturer of the APU).”
Upon review, no auto shutdown nor any failed attempt to restart the APU was recorded. Could the ECB have failed to record the incident? Unlikely. It recorded minor issues before and after the event so it was functioning properly. Diehl sent the ECB back saying no problems were found, and that ECB went back into service with no further issues. The APU apparently was working just fine.
But what about the radio not working? Was there an issue preventing that from functioning properly? Well, that assumes that the APU did shutdown. All we know for sure is that the APU didn’t automatically shut down. But as US Airways notes in the letter, “the ECB does not record a ‘commanded’ shutdown.” So maybe there was a commanded shutdown by someone on the aircraft? I have no clue because it’s not spelled out, but let’s assume that the APU was in fact shut down for one reason or another. What about those other issues that followed?
Apparently the airplane worked as designed. When on the ground, if the engines aren’t on, the APU isn’t on, and there is no ground power (basically, when the airplane is plugged in to a source at the airport), then the batteries will power many of the electronics. But there’s a catch.
To avoid completely draining the batteries while on the ground, the system will cut battery power when voltage drops below 23V for 16 seconds and the airplane is on the ground. When that happens, that VHF radio #1 won’t work. So that’s probably what happened here, and it worked as designed. Was the battery draining too quickly? Not according to US Airways. The airline says “the two main batteries were . . . tested by an outside source and have also been returned to the Company with no faults found.”
So the APU worked, the batteries worked, and the airplane in general seemed to work as advertised. The only thing I don’t see mentioned is anything about the “Hot Battery Bus” not working. The only mention of the hot battery bus in the letter is this:
. . . The [automatic battery shut off on the ground] will not disconnect the batteries when either one is discharged below 23V while in the air; they will continue to power the hot battery buses, DC BAT bus, DC ESSENTIAL bus, and the AC ESSENTIAL bus as long as possible.
So that seems to say that the bus (or buses), which provides continuous power to vital systems, was working. But no further mention is made beyond that. In short, US Airways says “this aircraft performed exactly as it was designed.”
Does that mean the captain fabricated what happened? I wasn’t there, so I don’t know. The only clue we have is from the US Airways letter which says “there is no discipline contemplated” after reviewing this incident. US Airways says it just wants to “put closure on the incident.”
It seems to me that if a pilot fabricated a maintenance problem, and it was proven conclusively, then that would be grounds for discipline of some sort, right? So since there is no disciplinary action here, maybe they’re chalking it up to a misunderstanding or confusion about the situation. Either way, it puts a serious hole in USAPA’s ongoing campaign to question the airline’s safety procedures.
[777 (not an A330) APU exhaust photo via Flickr user Robbie 1/CC 2.0]
