Fuel Number Crunching
 

As my FO and I were taxiing out the other day in EWR, we started pondering the point at which it's cheaper to run the engines vs shutting them down. Fuel seems to be creeping up rather quickly again, and with 25 planes waiting to take off, at what point does it make sense to just "shut'em down"? ATC seems to be pretty reluctant to give departure times, but sitting for 30 minutes just seems a bit much to sit and burn fuel. Any number crunchers our there with some "stats" for us?:confused:

We almost always taxi out on a single engine, and if ATC says it is going to be more than 10 minutes at a dead stop, most guys I fly with shut the other one down.

I was on jumpseat last year on a 767. We landed at ATL about 40 minutes early, and as you could guess... no gate available. We were sitting there for good 35 minutes, we had both engines and the APU running. This was back when the gas was 140 bucks a barrel. talk about a waste:eek:

Um ... anytime they're not running, they're not costing you anything. So, unless you need them running (you're next for takeoff or they're required for taxi), why would you have them running?

One other thing to consider: how much does an engine start cost? With the extra wear and tear, burning some fuel may be cheaper than multiple starts.

EWR had delays?


Personally, an eyeball test says run one engine and APU and constantly shut that one engine down but I don't have the numbers. The ERJ-145s had a place on the FMS you could look to see fuel burn per engine including the APU and there you could see how fuel increased substantially on the APU from it just running to being used for electrics to being used for both air and electrics.

That's interesting. How much wear and tear would there be for an engine that was started, running at idle speeds, and then shut down?

I don't know. These are answers a SMART management would provide its pilots. (Mine isnt that smart)

Back in my PT6 days, I think we calculated a start devalued an engine by about $60. With an idle burn of 150 lbs. per hour the break even point is about 40 minutes at today's fuel price.

Since fuel price is so dynamic, the number will change day to day. These calculations could be easily done by management and a note periodically sent to pilots. Then WE would have the TOOLS to reduce cost without affecting passenger service.

But why bother running a more efficient airline, just cut crew pay.

I never heard that starting an engine devalues it. I have heard an engine has so many cycles. I do not know how my airline defines cycles, but in the air force, a cycle was any takeoff, touch-n-go, or go-around (setting TRT).

So I wonder how much wear and tear there is on shutting down an idled engine. I have a friend who works for GE. I am going to call him to ask this question.

rewrite when I am not hungover