What happens when the lights go out?
Phrased one way or another, that is among the first questions to cross the minds of people unfamiliar with glass cockpits, but all too familiar with Microsoft’s notorious Blue Screen of Death.
It’s a good question.
Backup instruments are required by the FAA. How they are provided is up to the airframe manufacturers, to a very large extent, and some do it better than others. A very informal survey of glass cockpit airplanes suggests that most manufacturers hold a strong faith that the glass boxes never are going to go dark, judging from where they place the backups.
A builder of very popular glass cockpit singles puts the mechanical standby dials in a shelf below the pilot’s panel, at an angle requiring tall pilots to be contortionists. At the other end of the spectrum – in every sense – Raytheon’s current Hawker 800 backups are right at the top of the center stack, easy to see from either seat. The one thing these two airplanes have in common is that the backup instruments are small.
Eclipse may have found the best solution. An airplane built around its systems, the Eclipse 500 has so many built-in redundancies that there are no traditional standby instruments. The backups simply show up as a four-inch-square display on the 15-inch multi-function screen; a small replication of the airspeed, altitude, attitude and heading data normally shown on the large PFDs to the left and right of it.
Well, you may ask, suppose the MFD goes dark? Eclipse’s answer is that both engine-driven generators could fail and automatic load shedding would keep the standby package – and other vital systems – functioning for at least 30 minutes, on one of the airplane’s two batteries. To Eclipse, which has run very extensive tests, it seems unlikely to the point of impossibility that both PFDs and the MFD all could be lost at the same time.
The Eclipse solution avoids awkward placement of standby instruments, which is not limited to general aviation aircraft. Remember the Swissair MD-11 that crashed in 1998 after losing electrical power to a fire?
The Canadian Transportation Safety Board speculated that the pilot may have become disoriented while scanning between the standby instruments, placed very low, and the magnetic compass above the panel. The MD-11 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,” the board’s report read.
The board did not state, conclusively, that such disorientation caused the crash, but obviously considered it a contributing factor. Others have made similar speculations about a Cirrus SR 22 crash in Florida, last January. The SR 22’s compass, too, is in the usual spot above the instrument panel and the standby instruments are below the panel.
Pilots who fly with glass cockpits praise them extravagantly. The difficulties they report are two-fold: Learning to make use of all the information available, and transitioning back to round dials when necessary. Reliability is not a big issue, and rightly so. The failure rate of all-electronic systems is remarkably low, when compared to their mechanical and electro-mechanical counterparts.
But they do fail, which is why standby systems are required. Whether typical backups are adequate, or take ergonomics into consideration appropriately, is a matter that needs more careful consideration than many designers have given it, judging by their seemingly cavalier approach to placement.
The advantages of glass cockpits have not been lost on the avionics retrofit community. At every aviation trade show, companies are offering certified retrofit cockpits for a growing list of airplanes starting, naturally, with the older business jets. A lengthening list of installers provide retrofit capabilities which, as prices descend from the flight levels, are becoming affordable for smaller and smaller airplanes.
In fact, at Sun ‘n Fun, a Legend Cub was on display with a glass cockpit. Can gee-whiz technology for Light Sport Aircraft be far behind? When that day arrives, and ever more pilots are starting out in glass cockpits, adequate standby instruments – and their placement for ease of use under trying conditions – will be even more important than it is now.
Even in a Cub the lights can go out.
