Avionics News November 2014 - 22

SHIFTING REDUNDANCY GEARS
Continued from page 21

options exist to add a second alternator, and the easiest
imposes something of a sacrifice on the operator:
ditching the suction pump to make room for a standby
alternator. This entails swapping the two air-driven
gyros for two electric-system gyros. And the change
may well shave a little off the aircraft's empty weight
as it adds to the redundancy depth.
Besides, when has anyone heard a pilot lament,
"I sure miss those times when the suction gauge fell
below 3 inches."
With or without substituting electric attitude and
directional gyros, this simple alternative power
should preclude a multitude of system failure
stemming from electrical-system failure, and more
than enough to get them on the ground, safe and
sound.
Backup batteries:
The available range keeps growing
You need to only glimpse into a modern GAaircraft cockpit to see the transition from round
analog dials to digital-display instruments of various
form factors. There's no surprise here. The transition
means electricity plays a larger role in powering
today's flight decks.
This raises the stakes beyond merely needing the
electrical power to avoid needing the emergency gearextension system before losing even the landing light.
Most new-production aircraft equipped with glass
stacks arrive with systems designed appropriately for
their all-electric status: dual alternators or a standby
alternator; dual buses or a main and standby bus; two
batteries, often a main and a smaller standby model.
But the growth in glass comes mostly from owners
of older, classic aircraft who increasingly see modern
avionics and instruments as critical by flying with upto-date, late-model avionics. This switch may call for
more power than available from the original electric
system. Electronics drive everything - attitude to
airspeed to altitude and flight direction.
The decision to upgrade the electrical systems
makes a routine modification into the perfect time to
address adding standby-electrical capacity in the form
of a battery backup.
Increasingly, dedicated standby batteries can
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avionics news

november

2014

power digital components. Some avionics original
equipment manufacturers go so far as to equip their
products with integral backup batteries.
Several avionics companies offer standby batteries
of significant capacity designed specifically to power
avionics as a backup to the main-ship electrical
system. They just need a way to connect.
Take the next bus
To connect from one system to another, take the bus.
Combine a standby battery option with a backup
alternator, and the potential for a failure event to end
uneventfully increases significantly.
Whenever an owner opts to upgrade the electrical
system with some redundancy, however, the question
must also arise: How to connect this new redundant
power to components that need it?
Here, avionics shops can shine for the aircraft
owners. Help them design their standby-electrical
package to suit their needs and equipment.
Someone who simply wants the added safety of
alternator redundancy can get what's needed rather
simply when replacing air-driven gyro instruments
with electrically driven units. Put the alternator on the
suction-pump pad and wire the main and new standby
alternator to a regulator designed to handle both -
one that triggers a warning in the event of a mainalternator failure.
Then with an ammeter as a guide, the pilot only
needs to reduce the load below the limit of the
standby alternator - simple, effective and relatively
inexpensive.
Should the aircraft owner want more - a second
full-size alternator, for example - this approach still
holds merit.
But some pilots prefer something with simpler
management demands - understandable since
this equipment comes into play only because of a
system failure, something of a crisis even lacking
an emergency declaration. Simpler, from the cockpit
seats, involves both the standby power source and a
secondary or emergency power bus - with its own
switch.
Then when the main-alternator failure occurs and
the pilot shuts down the main electrical system, it
takes only a switch flick to bring up the standby
source, which, after a bit of advanced thought and
planning in the design process, connects only to the

Avionics News November 2014

Table of Contents for the Digital Edition of Avionics News November 2014