Avionics News July 2012 - 22

GOING GLASS

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STEP TWO – POWER SHIFTING: ELIMINATE SUCTION POWER FOR ELECTRON POWER Going glass in the cockpit provides an opportunity to add a dash of new and more-reliable redundancy to the ship by eliminating the much-maligned vacuum pump used to drive the attitude indicator and directional gyro compass in most planes. Many pilots consider suctionpowered instruments and the vacuum pumps untrustworthy, and a search for suction redundancy spurred a cottage industry grown up around providing alternative sources to drive the airdriven instruments. To add a degree of redundancy, the aircraft industry made the third gyro in the stack, either a turn coordinator or a turn-and-bank indicator, electrically powered. This is curious, since the idea of splitting instrument power between electricity and suction came about because of concerns with the reliability of both the instruments and their power sources. Of course, spinning-mass mechanical gyroscopic instruments were, at one time, the only solution, and their manufacture and reliability levels had appreciably increased over the years. Ditto for the much-maligned suction pump, a device so sensitive to the reverse rotation of an engine backfire that many pilots found their pumps failed within a couple of flight hours after a rotation-reversing backfire or spurious detonation. There are few crises greater for the instrument pilot than facing failed gyros because of the suction pump’s failure – or the parallel crisis of losing electrical power. Going glass in an airplane opens the opportunity to add electrical redundancy to a stack that, in most cases, will no
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longer carry any suction-powered instruments. Remember, if the panel’s all glass, it’s also all-electric. Losing an alternator or the main bus can mean flying with blank screens. Aspen covers the prospect of an electrical-system failure within most of its Evolution 1000 lineup: an integral backup battery capable of powering its host box for about 30 minutes. Mid-Continent Instruments and Avionics offers a line of standby power modules under its True Blue Power badge that can work to keep alive a variety of panel products, PFDs and MFDs, radios and navigators. Some pilots have embraced fieldapproved alternatives that incorporate a second charging source, such as a second, smaller battery and a standby electrical bus dedicated to powering a minimum of radios. B&C Specialty Products in Newton, Kan., offers STC’d standby alternator packages for a limited number of Hawker Beechcraft, Cessna and Piper designs. B&C’s BC410 standby alternator is standard on HBC’s G36 Bonanza singles and G58 Baron twins, and a version is STC’d for Bonanzas back to 1984 models. Automatic and seamless in picking up the power, it works through the main bus, providing an indicator that helps the pilot shed load until down to the capabilities of the standby source. Other solutions exist, including a standby electrically driven attitude indicator to back up the PFD – but, again, it still needs electricity. A ram-air turbine that drops from a wing also can provide alternative electrical power. Standby buses and second batteries are other options available, though likely more complicated and expensive than a standby alternator of some form. Regardless of the solution, some form of standby power seems prudent when electricity serves as the sole source of power to keep these

electronic wonders working. And, let’s not forget that the Federal Aviation Administration wants to see standby instruments next to the glass stack backing up the minimum: attitude indicator, airspeed indicator and altimeter. A multiple-screen, multiple-sensor glass panel can satisfy this requirement, but increases the importance of an alternate electric power source. Otherwise, you’re customer will need to accommodate the three instruments as stand-alone analog devices with no power needs. Help the client select both the best glass-cockpit system and the simplest standby power source, either for an allat-once install or a phased installation. Of course, with Aspen and MidContinent products, standby power is at the forefront and as basic as landing gear. And, should that main alternator fail, the B&C standby system automatically picks up 20 amps of load through its regulator, and an anunciator light will illuminate. Check the load meter in the panel and reduce load to 20 amps or less, and start looking for a suitable stopping point to determine the cause of the main alternator failure. STEP THREE – POST MODERNIZATION FAMILIARIZATION: TRAIN FOR THE TRANSITION, THEN GO FLY The beauty of the glass-cockpit PFD comes from its ability to consolidate and combine all the data from the six oldfashioned steam-gauge dials into one integrated display. Unfortunately, part of the confusion in using new technology stems from the ability to consolidate data from the six old-fashioned steam-gauge dials into one integrated display. Why? Because PFD instrumentation departs completely from the norm of those six round faces. For example, most PFD screens

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2012

Avionics News July 2012

Table of Contents for the Digital Edition of Avionics News July 2012