Friday, August 21, 2009

More Vague Pontification on Resetting CBs

As I said yesterday, anytime anything in the airplane emits smoke, fire or a burning/melting smell, it should be immediately turned off and its circuit breaker pulled and left that way until trusted maintenance personnel have examined it. Whether the behaviour led to a popped CB is irrelevant. There's obviously electricity going where it oughtn't.

Prior to the accident that started this discussion a pilot did exactly that. He wrote on the form provided for that purpose "Radar went blank during cruise flight. Recycled – no response ... smell of electrical components burning turned off unit – pulled radar CB – smell went away. Radar inop." That's pretty much what I'd do. Except that the 'radar inop' note might imply that he reset the CB and turned it back on to check. I would just assume that the release of the magic smoke heralded the death of the instrument. (Everyone knows about that, right? During the manufacture of sophisticated electronic equipment, little puffs of magic smoke are captured and held in various components. If at some point in the operation of the device the magic smoke escapes, that portion of the device will no longer work).

Pilots should not attempt to operate clearly non-functioning or malfunctioning equipment. One member of our fleet contains an old fashioned strike finder that doesn't work. It displays random blips of light but nothing useful. It's been placarded U/S for over a year. I fly it with the CB pulled.

The NTSB pointed out that:

Pulling the circuit breaker for the weather radar stopped a symptom (the burning smell) of the problem by removing electrical power from the circuit; however, it did not correct the underlying problem. Airplane electrical system anomalies that result in smoke and/or burning odors are indications of possible fire hazards. Moreover, the heat, smoke, fumes, and restrictions to visibility associated with an in-flight fire can represent a significant hazard to airplane occupants and adversely affect an airplane’s airworthiness.

The maintenance department told the senior of the two accident pilots about the weather radar problem, both by phone and in person, but the NTSB investigators believe that the other pilot probably reset the breaker as part of his preflight. His preflight should also have included reading the squawk sheet, as I believe Americans call the list of aircraft discrepancies. While some people might say that such resetting falls within the bounds of the "reset once" policy, I think it's a different matter entirely. If you find CBs pulled on preflight you should be finding out why. It may be as simple as asking your engineer "Hey Jan, did you pull the CBs for the lights here?" It's usual for engineers to pull breakers while working on systems and not unheard of for them to forget to reset everything.

According to Federal Aviation Administration (FAA) air traffic control records, about 0832:49, shortly after reaching a cruise altitude of 6,000 feet mean sea level, the ATP contacted air traffic control to declare an emergency, stating, “smoke in the cockpit we need…to land at Sanford.” The air traffic controller cleared the flight to proceed directly to SFB and descend to 2,000 feet. DAB airport surveillance radar data indicated that the airplane subsequently turned toward SFB and began to descend. The last radio transmission from the airplane was received about 0833:15. This transmission terminated midsentence and seemed to include the phrase, “shutoff all radios, elec[trical].”

That's startlingly fast. I too would try to make a quick radio call in busy airspace before making the airplane dark and silent. You don't know how long the two were coping with the problem before the initial radio call, but the accident was only ten minutes into the flight, so obviously not very long.

I agree with the conclusion made by the NTSB about the probable cause. It wasn't about circuit breakers.

The National Transportation Safety Board determines that the probable causes of this accident were the actions and decisions by NASCAR’s corporate aviation division’s management and maintenance personnel to allow the accident airplane to be released for flight with a known and unresolved discrepancy, and the accident pilots’ decision to operate the airplane with that known discrepancy, a discrepancy that likely resulted in an in-flight fire.

If you're flying an airplane that is flown by many people without a good means of communication of problems encountered, then you probably don't want to reset something even once. If you fly the same airplane all the time and you trust and communicate with all the others who fly it, maybe you do. If you have a journey log or a snag sheet do read through and see what has gone wrong lately, and what is still wrong that you might not want to accept. Reading this accident report and discussion has not made me uncomfortable with any of the times I have reset breakers. It has made me happier about the times I haven't. If it makes any difference to the people who disagree with our attempt to reset the flap CB a couple of weeks ago, we were on the phone to maintenance at the time and that was the first thing they asked.

Of course it's different for them because they are usually on the ground and can run away. As the report says, "An in-flight fire, especially one located in front of the pilots and directly over their legs, would be very distracting." And I thought the faulty gauge was distracting!

Also, this is very relevant to me. I long to tear out the entire dashboard and start over in so many of the planes I have flown.

Postmanufacture electrical system modifications and installations often result in general aviation maintenance personnel performing critical work among densely packed layers of wiring of different ages and materials

And I can always be wrong. The report says that "the ATP’s instructor stated that the ATP was “highly qualified,” required little or no academic instruction, and showed “exceptional” proficiency during his two simulator sessions. As I read that I thought, "That's what I want people to say about me." And then I had to add, "But not under those circumstances."


nec Timide said...

Thank you for your take on this. While I agree that resetting the circuit breaker in the accident air plane is a possible cause, I find it difficult to assign a metric that would give a usable probability figure to that. A second possible cause, one that the NTSB only addresses obliquely, is that Postmanufacture electrical system modifications and installations in addition to age and damage done when the weather radar threw a tantrum left the wire bundle with just over an hour of useful life. I think this is the idea that has lead to reset once theorem deprecation.

I also disagree with their assertion that GA pilots are playing whack a mole with circuit breakers. That just doesn't jive with my experience, AOPA publications notwithstanding, though I admit my experience is not universal.

A Squared said...

I also disagree with their assertion that GA pilots are playing whack a mole with circuit breakers.

That description made me laugh.

On a related note; I have toured the Whac-a-Mole factory.

A hangar neighbor years ago was the corporate pilot for the company and took me through the operation.

Frank Van Haste said...

Dear 'Trix:

I appreciate your two thoughtful posts on the CB reset issue.

There is, I guess, still a little daylight between where I net out and where my friend nec Timide does. My new default is to leave tripped breakers tripped unless there is an awfully good reason to do otherwise.

By the way, BTDT on the "shower-of-sparks-under-the-panel" deal. It was on takeoff roll in a 172 so I RTO'd and killed the master. No breakers tripped. A piece of aluminum bracing had come adrift and dropped across the primary bus. It does get your attention.



Anonymous said...

If the breaker tripped itself, and you reset it, and the same fault's still there, the breaker will usually trip again. So it's reasonably safe to reset it once to find out if there's really a fault or not.

What the NASCAR guys did was reset a breaker that'd been pulled by the previous pilot because he thought something was overheating WITHOUT tripping the breaker. Then, if you reset it, it'll go on overheating without tripping the breaker - which it did.

So, IMHO, the reset-once rule is fine for auto CBs but not for decisions made by other humans.

In hindsight, of course.