The APU Problem: A Quantified Approach

How much difference would using ground-based equipment make?
Switching off aircraft APUs while on the ground requires connecting to ground-based power and, when needed, preconditioned air units upon arrival at the gate. Both operations take little time. The APU, then, need not be turned back on until five minutes before pushback from the gate, to power up sufficiently to start the main aircraft engines.

Again, the clearest way to express the dramatic difference made by this reduction in APU usage is through numbers. The fuel savings alone should have the airlines clamoring to get this equipment in operation at every gate they fly into. See table 2.

An unexpected side-effect is the unbelievable noise-reduction at the airport. The ground-based equipment is typically 15-25 decibels quieter than the APU.

What issues are limiting the use of ground-based equipment?
Laziness. It only takes a button in the cockpit to turn on the APU. Ground equipment operation requires the handling of power cables and hoses between the ground-based equipment and the aircraft. Several of the U.S. airlines have figured this out and put major initiatives in place to get the equipment operated and are reaping millions of dollars in savings, not to mention the political benefits of environmental “pats on the back.”

Who wins when APUs are shut down?
There are, indeed, a long list of critical reasons to shut down APUs — safety reasons, regulatory reasons, air quality reasons, noise level reasons, even ramp congestion reasons (bridge-mounted ground power and preconditioned air units mean fewer vehicles moving around in close proximity to aircraft and, thus, less potential for aircraft damage).

But, reflection on a single economic observation suggests the potential scope of all the other advantages to be gained. The observation from a major airline chairman, which appeared in their own in-flight magazine, “For every penny a gallon that our fuel costs increase,” he pointed out, “the bottom line suffers by $27 million a year.” For those of us mathematically challenged, just think of the opposite effect by saving the entire gallon of fuel.

Who wins when APUs are shut down? Everyone who works in the commercial aviation industry. Everyone who flies or relies on shipments by air. Everyone who breathes. In short, everyone.