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Misusing, Confusing and Disabusing the MEL

Air Safety Week, July 2, 2007

A Perfunctory "Press on Regardless" Turns Nasty

The aircraft, an Airbus A319, was dispatched under the provisions of the operator's Minimum Equipment List (MEL) with the Auxiliary Power Unit (APU) generator on line, substituting for the No. 1 main generator, which had been selected off after a fault on the previous flight had caused it to trip off- line.

During the cruise, the APU generator disconnected from the system, probably because of a recurrence of the original fault. This caused the loss of a substantial number of aircraft services, including many flight instruments and all means of Radio Telephony (RTF) communication.

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In theory, manual reconfiguration of the electrical system should have recovered many of the services, but the flight crew was unable to achieve this. Since they were without RTF communications, the crew considered that the best option was to select the emergency transponder code and continue the flight in accordance with the flight plan.

On the prior sector from Stansted to Alicante, Spain, the #1 Integrated Drive Generator (IDG) had failed. Attempted resets were unsuccessful. Approval was available for redispatch under the MEL with IDG1 selected off and with the APU (not normally left running) to provide generator services in lieu. It was supplying the Main AC busbar #1 (AC1) and IDG2, the other engine-driven generator, was powering AC2.

In the cruise at Flt Lvl 320, the crew heard a clunk and lost multiple services and systems. These included all the captain's flight instruments: Primary Flight Display (PFD), Upper Electronic Centralized Aircraft Monitoring display (ECAM), and the Multi-purpose Control and Display Unit (MCDU). The autopilot kicked out with an aural Master Warning alarm tone, autothrust was lost (also triggering an aural alert).

In addition, many illuminatory lights were lost. That's no big deal in daylight, but it would be at night. Of more concern was the loss of all lights on the overhead panels. It just "went dark". This meant not only the illuminatory lighting but all integrated captions.

Consequently, if a warning (RED) or caution (AMBER) or advisory (GREEN) caption would have been illuminated to indicate a further systems loss or deficiency (which was likely under the circumstances), no such advice was available and no further correspondence was to be entered into.

The center pedestal lighting and captions similarly went to sleep. Such sweeping multiple electrical failures in an all-electric jet would have gotten the crew's rapt attention. There's no mention in the report about what might have been happening aft of the cockpit door.

The copilot, noting that the Commander no longer had any flight instruments, assumed control. He ascertained that the FBW (fly-by-wire) aircraft was now in a reversionary Alternate Law mode. The captain started running the appropriate checklist. He pushed the AC Essential Feed push-button but this had no effect.

He also noted that its integral caption was dead so he couldn't discern whether its pre-push status had been NORMAL or ALTERNATE (all the captions were dead, remember?). Can one have faith that the button's electronic function is still available in such circumstances? Might this be considered a design dichotomy?

The conundrum deepened when the pilot tried to transmit a Mayday call. He tried VHF1 and VHF2 but obviously his own Radio Management Panel was dead. The copilot tried his and then they tried the Observer station's (i.e., jump-seat) VHF3. All were dodo'd, as in "dead as a .."

In such circumstances, it's not unknown for a crew to transmit "in the blind" on the assumption that the loss of receiver side-tone (only) may be the problem (as in it being muted or oversquelched) and that a one-way comms transmission is way better than no comms at all. Perhaps a passenger's cell- phone might have been a fall-back solution?

Pressing on with the ECAM actions, the pilot selected ATC2 (the alternative ATC transponder) and dialed up the Distress code of 7700. This at least (he hoped) would cause the bells to ring and captions to flash on ATC radar screens along his route of flight. ATC would keep the flight cocooned in an airspace bubble and assume that the low-cost flight was either in electronic limbo -- or into big-time savings on its electricity bill.

The crew's selected course of action was to fly the flight-plan to destination, although they'd have no updated weather for it. When the gear was selected down it failed to extend, but the mechanical drop system worked, although reassuring indications were still very sparse. A safe landing was made at Bristol despite the cumulative deficiencies.

In the Airbus system, a Generator Control unit (GCU) monitors the IDG's outputs and opens a GLC relay (Gen Line Contactor) if it detects an out-of- limits condition (volts/amps/cycles etc). Selecting a GEN to OFF also opens said GLC. In the event of IDG failure, the APU Gen can contribute to the load via a BTC (Bus Transfer Contactor).

Government Industry

Misusing, Confusing and Disabusing the MEL

Air Safety Week, July 2, 2007

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