In an era of glass avionics, standbys sometimes ignored

 - November 1, 2006, 9:09 AM

Today’s highly capable glass cockpits certainly put old, round-dial standby instruments in the shade. In many cases, standby training has become almost a chore rather than a necessity. Yet the standbys are always there, ready for us. The question is, are we always ready for them?

Edited extracts from a preliminary NTSB report on the fatal accident of a Cirrus SR 22 in Florida last January suggest different answers. Mid-morning visibility at the accident site was 5 to 10 miles in light rain and mist, with a 600-foot ceiling.

A witness stated that he heard an airplane above the clouds that sounded as if it were conducting aerobatics, climbing and descending. Suddenly, it descended out of the clouds, then banked and headed back up into the clouds in a northeasterly direction. As it ascended, the witness heard  “an rpm change, like it was climbing.” The pilot’s last message was  “I’m losin’, I’m losin’ it again here.” The witness then heard the engine get louder, followed by the sound of an explosion.

Glass-cockpit Flying

The owner-pilot had 483 hours total flight time, including 405 hours in glass-cockpit SR 22s. He had 15 hours of actual instrument time and 61 hours of simulated instrument time, and within the previous 30 days had flown two ILS approaches, one VOR approach and one GPS approach, accompanied by an instructor, with one approach on partial panel without the primary flight display (PFD). The pilot had also practiced partial-panel “a number of times before,” according to the instructor.

The PFD included airplane attitude, airspeed, heading and altitude, a horizontal situation indicator and a vertical speed indicator. Below the PFD, on a “bolster panel” in front of the pilot, were backup altimeter, airspeed and attitude indicators, to be used “in case of total or partial PFD failure.” Maintenance records showed that the PFD had been replaced on June 4, 2004, at 12.2 hours, on Sept. 14, 2004, at 55.2 hours, and on Dec. 20, 2004, at 80.6 hours.

Quite properly, the NTSB didn’t draw any conclusions in its preliminary report, since any number of causes might eventually emerge. Yet many might reasonably conclude that the owner, having minimal instrument experience and in poor weather, may–despite the worrisome maintenance history of his PFD– have been relying totally on its possibly incorrect or failing data and ignoring his standby instruments, which might have saved him.

Possible Disorientation

Yet there may have been a quite different reason. The pilot actually might have been coping fairly well using the three standby units at the bottom of his panel. He might have become disoriented when he looked up at the compass in its traditional location below the top of the windshield.

Unreasonable? In its report on the 1998 crash of a Swissair MD-11–which lost all electrical power to the flight deck at night due to a fire and had a similar stand- by instrument/compass con- figuration–Canada’s Trans- portation Safety Board noted that “the MD-11’s compass required a considerable vertical scan to complete an instrument cross check, thereby risking coriolis illusions from large up and down head or eye movements during turns, which can produce severe disorientation, even among experienced pilots.”

While the Board cited this effect as only a possible contributing factor, not the cause, of the accident, it pointed out that “the result could be disorientation of the flight crew and loss of control.” It added, “The challenge of flying using standby instruments would be even greater for flight crews who were not well trained in their use.”

A Canadian investigator later told AIN that when he attempted to make accurate turns in IMC using a similar standby instrument/compass configuration, he experienced moderate to severe vertigo, with frequent departures from level flight. Subsequently, Swissair installed combined standby attitude, airspeed, altitude and heading displays into a single “Basic T” package in its MD-11s, and instituted more rigorous standby instrument training for its pilots.

There’s no question that glass cockpits have changed the way we fly. However, a nagging question remains: can we fly without them?