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Never Again Online: Mission criticalNever Again Online: Mission critical

Pelting rain pounded the Piper Aztec as it labored through the scud. The airplane was on a ferry flight en route to Thunder Bay, Ontario, where our crew would rest up for a night before flying to Geraldton to begin its aerial photo mission in northern Ontario.

Pelting rain pounded the Piper Aztec as it labored through the scud. The airplane was on a ferry flight en route to Thunder Bay, Ontario, where our crew would rest up for a night before flying to Geraldton to begin its aerial photo mission in northern Ontario.

Only an hour before, the three of us (two aviators and a camera operator) were finishing the installation of the airborne photography equipment and exhaustive ground checks of the elaborate hardware. This would be no ordinary aerial surveillance operation but rather a large-scale photography (LSP) flight, which is different from conventional high-altitude photography. For one, LSP operations take place at less than 1,000 feet agl, and they can be conducted under cloud cover in low light. In contrast, conventional small-scale photo ops (photos covering large areas of ground) have to wait for horizon-filled days with unlimited visibility and skies clear of clouds. A highly experienced crew, we suffered very little weather-related downtime, often gearing up to fly while our grounded high-altitude brethren looked on.

The flight originated in Pembroke, Ontario, where the customized camera mount was installed over a camera hole in the belly of the aircraft. The swivel frame held a laser and two Vinten cameras, one with a wide-angle lens that was used for accurately orienting the photo (survey) lines onto topographical charts, and the other with a telephoto lens that shot the actual survey lines. The laser measured photo altitude.

The system and crew had a history of working well together. The captain was an experienced airline transport pilot, I (the navigator) had a commercial pilot certificate, and the camera operator was an aerial-photography veteran. Most flights to and from jobs were under IFR, while photo ops took place under VFR. The airplane had to be hand-flown at low level and in slow flight during photography — an autopilot could not handle control inputs quickly enough when commanded by the navigator. All photo navigation was done using sectionals and topo maps without the aid of GPS or loran (at the time, general aviation's use of GPS was in its infancy). Remarkably, more than 98 percent of our aerial photographs were fully on track and usable by photo interpreters.

The Piper Aztec was a bulletproof airplane highly respected by the crew. Fitted with long-range fuel tanks, six in all, it had incredible endurance. It had a responsive slow-flight envelope and was a safe twin that was a pleasure to fly. It had never let us down in previous missions across Canada, flying into and out of rough airstrips and in all types of weather. Not unlike bomber crews of World War II, we had to endure cold weather since all photo ops were conducted with an open camera hole (the laser beam could not penetrate glass or plexiglass), which rendered the heater ineffective. We often flew photo missions for up to six hours in freezing cockpit temperatures before returning to base. There was no way to replace the hatch cover in flight.

On this evening, there was no indication of the problems to be. Anxious to take off before darkness fell, the cameraman and I stowed the crew's gear while the pilot conducted a thorough walkaround. A trough of low pressure over Lake Superior was bringing rain to most of Ontario, but it hadn't yet affected the Ottawa Valley except for low ceilings. Both engines started without undue hesitation and all instruments and electrical checks proved normal, save one. The ammeter indicated a hairline discharge, probably a result of the loads placed on the electrical system during the LSP equipment checks prior to startup. No problem, we thought. The engine alternators would quickly bring back the charge.

The runup indicated all systems go. This would be a routine IFR flight with heater and hatch cover on. The airplane was in the soup within minutes after takeoff. The pilot was busy preparing to reach cruising altitude as I settled in for a nap and the camera operator flicked on his reading lamp.

About 30 minutes into the flight, the rain started and it began to get noticeably darker inside the airplane. This wasn't unusual since night was approaching and the aircraft was in clouds. However, the ammeter persisted in reading a more pronounced electrical drain that troubled the pilot. It also seemed as if the instrument lights were not as bright as they should be. Was the ammeter malfunctioning or was there a short somewhere? He checked the circuit breakers. Were the alternators acting up? One by one he tested the electrical loads to isolate the problem. Nothing remedied the situation but one thing was now clear: The aircraft was suffering an electrical failure.

The pilot immediately assessed the risks without alarming his crew. On instruments at night, in rain, and somewhere over the Algonquin Highlands, the pilot roused me. The backseat cameraman knew something was amiss, immediately poking his head between the pilots' seats to listen intently.

All on board were calm. The pilot explained the situation. The engines appeared healthy with plenty of fuel in the tanks. The loss of electronics meant flying the airplane with engine-driven, vacuum-powered primary flight instruments. The most precious, electrically dependent gauges were the radio navigation aids. With reference to these, the pilot could divert to the nearest instrument airport and let down through the scum.

All ancillary power drains were immediately shut down, including external navigation lights, anticollision beacons, internal post lamps, instrument illumination, heater, and autopilot. The pilot could barely hear air traffic control. The system was failing fast. He turned down the volume to conserve precious power, dialed in 7600 on the transponder, and called in the emergency. The situation was becoming critical.

Noting the time, the pilot headed to North Bay. He studied the airport's approach plates while I held a flashlight, periodically directing the beam toward the panel when instructed to do so. The crew tightened its seat belts as the rain intensified, sounding like marbles bouncing off the windshield.

The pilot slowed the Aztec to its maximum landing gear extension speed and felt the wheels lock with confirmation from the three green indicator lights. It would be one less thing to worry about. The pilot decided to refrain from transmitting and maintained a listening watch for ATC's reassuring instructions as the controller painted the Aztec's position and cleared it for an emergency descent to Runway 26. If the radio failed completely, he was totally dependent on his navaids for the instrument approach. Were they trustworthy? He prayed they would work until the runway was in sight; otherwise, their dilemma would be grave.

This would have to be a perfect approach — missing it could be deadly. I dutifully shone the weak flashlight beam on the instruments while straining to see through the murk. There was a profound cockpit silence despite the roar of the engines and clatter of driving rain. We didn't feel desperate or doomed but rather highly focused on the task at hand.

Time's passing seemed eternal when I suddenly noticed the wall of gray in front of us brighten. What I saw next I would never forget. Within milliseconds the cockpit was bathed in light as two rows of intense white lights appeared no more than 300 feet below the illuminated ceiling that was reflecting a radiant glow on the wet surface.

The flight service specialist had turned up the runway lights to maximum power to aid our stricken aircraft. The pilot's approach was flawless as the airplane touched down smoothly in the rain. As we taxied to the apron, emergency vehicles surrounded the aircraft.

They weren't needed — the emergency was over.

That night, a quick check of the aircraft's manual found the problem. Apparently the alternators would not kick in if battery power was depleted below a threshold amperage. This condition was created during static ground checks of the camera equipment, which resulted in alternator shutdown. The ammeter reading was correct but so borderline that its warning was misinterpreted. The battery was charged overnight and the mission continued the next day without further incident.

The lessons we learned were invaluable. No matter how insignificant a problem appears, it's still a problem that can lead to disaster. Know your systems and the significance of their impact on the mission.

Paul V. Tomascik, AOPA 4942424, is a commercial pilot with land and sea ratings.

Additional information on electrical system malfunctions can be found at the following links:

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Posted Thursday, May 06, 2004 12:50:02 PM

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