I'm quite sure the device will be powered by the APU, which will
produce electricity and air conditioning for all the equipment, and the
pressurized air needed to start the engines later.

An idling jet engine uses a TON of fuel and makes quite a bit of
thrust; aside from initially getting the plane moving, taxiing is
normally done at idle thrust anyway. But it's that high idle fuel
consumption that this will eliminate for the taxi-out, and I think it's
a terrific idea.

Just to throw some numbers out, an older 737's engine (I don't have
specs in front of me for the newer ones) burns about 1200 pounds of
fuel per hour, per engine, at idle.. The APU burns about 300 pounds
per hour. A savings of 900 pounds, or about 135 gallons of fuel per
hour over a single-engine taxi. (315 gallons less than a more-common
two-engine taxi!)

Jet fuel's costing the airlines upwards of $1.75 a gallon. For every
minute the airplane could taxi using only the APU instead of one
engine, an airline would save about $4. A typical 15-minute taxi-out
at a semi-busy airport would save $60. An hour-long taxi on a bad
weather day? $240.

Obviously the economics will be different for each airplane type, and
for some airlines like Southwest that don't normally fly into
delay-prone airports, it might not make financial sense to install this
device.

But an airline that flies to LaGuardia, Chicago O'Hare, Atlanta, etc.,
all day long? It could save a ton of money if they can make it work.

--
Garner R. Miller
ATP/CFII/MEI
Clifton Park, NY =USA=