Avionics News May 2013 - 22

What Does a Pilot Have to Lose – Aside from Life?

POWER REDUNDANCY
Continued from page 21

General Aviation’s Evolving Electron Appetite

In a way, aviation’s increasing appetite for electron flows
mirrors that of American society at large, and it tracks with the
boom in digital electronics and software-managed systems.
So used to thinking of electricity’s role in automotive hardware, most lay people express significant surprise upon learning that most piston aircraft engines need no electrical system
to run; no battery, no spark coil or computer management, in
most cases.
Instead, dual-redundant engine-driven magnetos provide the current source that’s boosted into the hot blue
spark of the plugs.
Thousands of the earliest planes were built and flown
without as much as a post light. As aircraft developed,
however, equipment needs grew; lights, in the great
scheme of things, may sound like the most flight-critical.
Far from it.
Electric lights helped enable night flight by illuminating
runway ends and edges. Shortly after, airborne electricity
made possible airborne radios for communicating with
other aircraft and ground stations – even ships at sea.
Gyro instruments like the attitude indicator, turn and
bank indicator and gyro compass, or directional gyro,
made instrument flight not only possible, but routine.
The design that split gyro power between air and electricity made instrument flying a bit more reliable.
For many decades, loss of electricity cost an aircraft
one gyro: the turn indicator… and any and all communication and navigation radios and lights. Losing suction was
the scarier scenario with air powering both the attitude
indicator and directional gyro or gyro compass.
With today’s shift toward digital glass instrumentation,
it’s common to find airplanes with everything in the panel
needing a continuous flow of electrons. The demand on
main-ship batteries often rises with the sophistication of
the panel – particularly for the all-electrical airplane with
an all-glass panel and electric autopilot.
The solid-state attitude sensors need electricity; ditto for
the video screens of primary flight displays and multifunction displays, digital-electronic VHF navigation and communication radios, GPS navigators, transponders, ADF,
DME – the works.
Even with the trio of standby flight instruments the FAA
wants in glass panels, a total-electrical system failure for
an airplane with such a panel is a serious crisis – an emergency with compound problems and serious implications
for the pilot-in-command.
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Let’s not spend time sugarcoating this: A total electricalsystem loss in an all-glass airplane may rank as a nothing
burger to those who seldom fly at night, rarely indulge in
flying IMC – and never fly night/IMC. They are practically
fair-weather day/VFR-only flyers. This pilot likely sees a
redundant suction source in the same light – nice to have if
you do that kind of flying, but…
Still, many of today’s cutting-edge aircraft sport cuttingedge glass stacks – and their pilots bought the plane and
earned the ratings so they could pick up more flyable days
when they needed to travel.
Lose the electron flows, and attitude-reference systems
stop referencing the horizon; radios and air-data instruments
all go away; and lights go bye-bye.
That’s why today’s most modern all-electronic-panel birds
come from factories smart enough to build in redundancy.
But with the increase in retrofit options for everything from
CAR 3 antiques to Part 23 business-turbine airplanes, thousands of airplanes receive new panels each year.
Redundancy should be added to allow these pilots a fighting chance after a total-electrical-system failure.
Lose electrical generation in a glass-cockpit airplane…
well, the depth of the problem can not, in this pilot’s view,
be overstated. And neither can the wisdom – make that the
necessity – of electrical-power redundancy.
Not only do we enjoy redundant options for electrical redundancy, we have multiple levels of redundancy capabilities
available. Shops can help pilots understand the limitations of
their electrical system, gain an understanding of the expected
battery life in the event of a generation-source loss and help
them understand that scenario in terms of minutes to dark.
From there, shops can help a pilot or owner understand the
essential need; the available options; their costs; their benefits – and their minuses. Consider some of the many ways
available to equip an aircraft with a redundant electricity
supply.
Second-Generator Solutions:
Full-power or Standby?

One option popular with many pilots is a second alternator
driven off the engine.
Some airframe companies build their planes with system
redundancy consisting of a smaller-capacity alternator and a
regulator that senses the main-alternator failure, loads up the
standby alternator through the main bus, and simultaneously
illuminates a cockpit warning light so the pilot can shed load
on the alternator by shutting off nonessential equipment.
Other solutions in use include a second main electrical bus
with its own full-capacity alternator standing by to pick up the
load upon the failure of the first, identical electrical system.

Avionics News May 2013

Table of Contents for the Digital Edition of Avionics News May 2013