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On Becoming Electrically Inert

Air Safety Week, July 2, 2007

Switches that Kill

After takeoff and in instrument conditions, at a point six minutes after takeoff, the pilot of a Beech 200 KingAir progressively lost his EFIS instrumentation (Proline 21 avionics) and all communications.

He assumed that he had a major avionics failure and concentrated on the standby flight instrument display indications until the aircraft had climbed clear of cloud and was level at FL150.

Scottish ATC became aware of the aircraft's predicament when they saw its tracking change and lost its transponder signal and all comms. They dispatched a Tornado fighter to intercept. After some confusion, the KingAir followed the fighter but then lost control upon entering cloud.

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Reason? The backup standby flight instrumentation was also EFIS and it too had ultimately failed.

The Tornado made a Mayday Relay call and vectored back onto the aircraft, a short while later finding it flying between cloud layers. A passenger aboard the KingAir contacted ATC by cellphone and ascertained that the plan was to recover them to Leuchars.

The KingAir was guided clear of cloud to a successful visual approach and landing at RAF Leuchars on the East coast of Scotland. The aircraft had been airborne for almost two hours and had been without electrical power for at least 90 minutes.

Technicians at Leuchars applied ground power and could not fault the aircraft. Investigators later analyzed the timings of the progressive failure and factually deduced the likely cause. The pilot was the Chief Pilot and he normally flew the Beech 200 fitted with electromechanical instrumentation.

There was no requirement for him to "convert" to the ProLine 21 version (see displays at tinyurl.com/367fzp). However, he had right-seated about 10 times for another pilot. Climbing into the LH seat he had actually been entering an alien and unfamiliar environment with respect to the switchology layout and displays.

Once the emergency commenced, the pilot considered that the workload involved in maintaining the standby instrument scan for controlled flight had made fault finding "almost impossible". This is a classically common observation for single-pilot IFR flight emergencies.

After the flight, he stated that he had seen no warning or caution lights illuminate while airborne and he could not recall whether he had checked the voltage/loadmeter gages or the battery ammeter gage during the flight. Once on the ground, the commander checked the battery voltage and noted that it was very low.

There was no data recorder and the CVR had been overwritten, so investigators relied upon the recorded Radar times and R/T transmissions. There'd been only six minutes between takeoff and the loss of the aircraft's secondary radar return. The KingAir has a 28VDC starter-generator on each engine, two main batteries and a single NICAD battery for backup instrument power.

The Generator field switches are situated to the left of the control column and sit beneath a guard labeled "master switch". If a GEN trips, the switch must be moved up to a spring-loaded reset position and released. Unguarded engine auto ign, engine anti-ice and ignition and engine start switches are clustered near the generator and battery master switches.

These switches are not visible to a pilot who's in (and previously only flown in) the right seat. Battery Ammeter and Load and Voltage meters are located in the overhead panel. A sole pilot experiencing flight instrument woes would not want to look up and back at them, because that would be vertigo inducing. The pilot did recall looking down at the battery and generator switches and seeing that they appeared to be on.

As there were no indications of a GEN trip, he did not attempt any GEN resets until much later, just before landing when the gear wouldn't extend. A failure of either/both generators should illuminate the master caution light together with an associated L GEN and/or R GEN amber caution caption(s).

The only other advisory, besides the meters, that there is an electrical failure underway would be the amber caption on the caution annunciator panel and there are two traps connected to actually "seeing" that. Some caution panels have a caption bright/dim switch but many other annunciator panels automatically go to DIM if a night-lighting rheostat is turned on (or is left ON from a prior night flight).

In some aircraft, even if a single rotary rheostat is just "cracked", the caution panel lights will dim and be virtually invisible for daytime flight. The other trap is that the caution panel's captions dim progressively as it's also inevitably affected by any electrical failure and a consequent flat battery, i.e. it may display the caption for five minutes maximum before "light's out".

Initial actions upon receiving a RED MASTER WARNING or amber MASTER CAUTION is to cancel it and then look down to identify the malfunction's caption. However, in the circumstances described above, a lit caption will simply not be visible. The pilot will naturally assume a transient self- correcting fault condition had caused the MASTER to flash.

Government Industry

On Becoming Electrically Inert

Air Safety Week, July 2, 2007

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