MD-82
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Distraction; Training / Qualification; Troubleshooting; Workload; Time Pressure; Human-Machine Interface; Confusion
Aircraft Equipment Problem Critical
Flight Crew FLC Overrode Automation; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; Flight Crew Took Evasive Action; General Declared Emergency; General Maintenance Action
Human Factors; Environment - Non Weather Related; Aircraft; Manuals
On this leg; the First Officer would be the pilot flying and I would be the pilot not flying. Gate departure; taxi-out; takeoff; and initial climb were routine until approaching approximately 22;000 FT. At that point; the aircraft electrical system began to cycle on and off very rapidly with random indicator lights illuminating repeatedly. These lights were activating on both sides of the aircraft cockpit indicating both left and right electrical systems were involved. Various aural warnings were also activated. Flight instruments on both sides were useless as the screens cycled on and off. ATC communication was no longer available since the audio was cutting rapidly in and out. The Lead Flight Attendant knocked on the door and yelled through the door vents that the lights in the cabin were cycling on and off. I remembered that the first step in the Intermittent AC Power Interruptions checklist was to move the AC Crosstie Switch to the OPEN position and attempted to do so. The distraction was so strong I actually had difficulty finding the switch. Eventually; I located the switch and turned it to the open position. To my complete amazement and befuddlement; nothing happened. The lights and noise continued unabated. This extreme noise and confusion was so great I determined it would have to stop before we could address the problem. I was also becoming concerned an electrical malfunction of this magnitude could result in an electrical fire. Apparently the First Officer had the same thoughts and suggested turning off the generators. Since we were in clear and visibility unlimited meteorological conditions; I concurred and turned the right generator switch to off. It had no effect except to de-power some instruments on the right side of the cockpit. The noise and confusion continued so I turned the left generator switch to off and the lights and noise ceased. I confirmed the Emergency Power Switch was On which restored basic instruments on the left side as well as ATC communication. Emergency power was stable. I advised ATC of the situation; declared an emergency; requested a descent; and told them I would give them more in a minute. ATC acknowledged and gave us an initial descent. We both agreed that landing as soon as reasonably possible was the best course of action. I was concerned both that an electrical component may have been burnt and that we had only 30 minutes of battery power remaining. We briefly discussed a nearby airport as a possible landing location due to its close proximity; however; I concluded a return to the departure airport would be best since we were familiar with the airport; had approaches and charts immediately available; and knew it had a very long runway. The long runway would be preferred if we had to land with emergency power only. Also; the difference in time would be very small. I asked the First Officer if he would prefer I take the aircraft since he was now flying cross-cockpit on my instruments. He stated he would prefer to fly and flying cross-cockpit would be no problem. Again; considering the excellent weather; I concurred. We then divided duties; the First Officer flying the aircraft and communicating with ATC; and I handled the checklist and other tasks. The First Officer began working with ATC and I made an extremely brief announcement to the cabin stating we had a major electrical malfunction and would be returning to land. At that point; I considered two checklists which could apply. First; the Intermittent AC Power Interruptions checklist might have been appropriate if the electrical system was still powered. I also reasoned that since opening the AC Crosstie did not stop the problem this checklist would not be helpful. Instead; I selected the Complete Loss of AC Power checklist; which was our current situation and greater emergency. As I began to work through the checklist; my workload increased radically due to the requirement to operate the pressurization manually. The increased workload made an enormous difference in my ability to accomplish other tasks. As I reached the point in the checklist of attempting to restore the AC electrical system; I considered the potential ramifications of such an attempt. I realized it may bring back the lights and noise or; it could give us back many needed electrical components. In the end; I felt an attempt to restore the AC electrical system should be made. I advised the First Officer of my plan then reset and turned on the generators; one at a time. Each generator properly powered its isolated system. With AC electrical power restored; I breathed a sigh of relief and advised the First Officer. I also made a call to ATC advising them that power was restored; but we still wanted to proceed to our departure airport to land as a precaution. I also made an extremely brief announcement to the cabin that normal electrical power had been restored; but that we were proceeding to the departure airport to land as a precaution. Concurrent with the final word of my cabin announcement; both sides of the AC electrical system began to cycle again with lights flashing and aural warnings blaring. Since both generators had checked normal and the cross tie switch was open; I now believed there was a serious problem in the electrical system that was affecting both sides. I immediately turned both generators off and determined I would not attempt to restore the AC electrical system again. Instead; I was now committed to the remainder of the flight and landing on Emergency Power only. I returned to the checklist section 'If AC buses not restored;' and continued. Upon reaching 'APU - windmill start;' I reasoned there was no need to attempt an APU start since I would be unwilling to connect its power to the AC system. Further; we had two operating generators and; as best I could remember at the time; we were well outside the probable windmill start envelope. I therefore did not attempt an APU windmill start. We were now closing rapidly on the airport and I continued the checklist; calculating landing bugs; etc. Again; my tasks were slowed by the constant need to manipulate the cabin pressurization. I finally put the cabin in a gentle climb so it would depressurize and left it alone. My checklist tasks complete; I rejoined the First Officer as we turned final. He was doing a magnificent job of flying an aircraft that was well out of trim. As we began to configure the aircraft; I retook responsibility for ATC radio communication. As I selected the final flap configuration (flaps 15) for the First Officer; it occurred to me we hadn't run a before landing checklist. Rather than distract the First Officer who was fully engaged in flying the aircraft; I silently checked the position of the gear; flaps; etc. On about a five mile final; the First Officer was still approximately 40 KTS fast and the aircraft was slowing little. With no anti-skid available; I really wanted touchdown to be as near on speed as possible. We were less than flap 28 extension speed; so I advised the First Officer I was moving the flaps to 28 degrees to help us slow and if the trim got worse to let me know and I would put them back up immediately. To my surprise; I could not feel any difference in the aircraft's flight characteristics and wondered if the flaps had moved at all. I then moved the flap handle to 40 degrees figuring I would take what I could get. There was no obvious adverse trim effect and the aircraft began to slow. (In hindsight; I believe the flaps moved very slowly since they were only being powered by the engine driven hydraulic pumps). This allowed us to slow to the appropriate approach speed (for flaps 15) in plenty of time to make a stable approach. Touchdown was smooth; in the touchdown zone; and on speed. The First Officer was somewhat aggressive in his application of reverse thrust which initially caused some directional control issues; but recovered well. On touchdown; I inadvertently did not manuallyextend the spoilers. We came to a final smooth stop with approximately 4;000 FT of runway remaining. I immediately made a PA commanding everyone to remain seated. I positioned the flaps to 28; checked spoilers retracted and parked the brakes just in case we needed to evacuate. We then shut down both engines. We contacted the Airfield Rescue and Fire Fighter crews on the discrete frequency provided who informed us we had one blown tire; but no other damage. I then contacted Ramp/Maintenance to begin arranging for transportation for our passengers. I then took a walk through the cabin greeting our passengers; reassuring them; and answering questions. Maintenance arrived at the aircraft; pronounced it suitable for towing and towed the aircraft; with crew and passengers to the gate. The aircraft battery died while being towed to the gate. Gate arrival and deplaning were uneventful.
The Reporter stated that his Company's Maintenance Department discovered the Right Generator Control Unit was at fault for this event but the Left Generator and CSD were also replaced. The Generator Control Unit relays were reportedly 'fried' and the generator would not drop off line even though there was a fault detected. The relay clicking sound was behind the Captain's seat but more distracting was the continuous aural warnings; flap; slat; stall; etc. The 'racket' was so distracting that the Reporter's cognitive function impairment prevented his motor responses from locating the AC Crosstie Switch which was located directly over his head and which normally he could find by reaching up without looking. He is still confused why both the Captain's and First Officer's instruments were affected and it was that confusion in the moment that also lead him to de-power the aircraft so that the crew could think and formulate a return safety to the departure airport.
[Narrative #2 contained no additional information.]
A MD-82 Right Generator Control Unit malfunctioned in flight locking the malfunctioning generator on line which resulted in rapid equipment cycling OFF to ON; all aural warnings to sound; and the inability to communicate inside or outside the aircraft. An emergency was declared and the flight returned on Emergency Power only.