The hidden cost of the ‘taxi delay’.
While our crew waited for our aircraft to arrive at JFK yesterday, the plane itself was already on the ground. However, it was parked on a taxiway for approximately 45 minutes as the crew waited for gate and ramp area congestion to clear. This type of arrival delay is not an ATC problem. It’s a problem with how individual air carriers manage their gates. However, due to this wait, our flight pushed 10 minutes late, which ultimately translated into arriving at our destination 35 minutes behind schedule.
For late afternoon departures out of JFK, each extra minute which is consumed getting off of the gate and into the departure queue, can expand a delay by a multiple. As is the standard (and very outdated) method of handling outbound traffic at airports all across America, aircraft are not sequenced for takeoff until the cockpit crew calls ground control for taxi to the runway. Any time which is spent trying to push-back from the gate, start engines, and leave the ramp area, does not count until the radio transmission calling for taxi is made. As a result, we were number 31 for the runway once we got clear of the ramp and were put into the departure queue by ground control.
At over-consumed airports such as JFK, where taxi delays like this can be anticipated as part of standard operations, extra taxi time is built into the flight’s published transit time to the destination. This allows flights to arrive ‘on time’ at their destination even though it may have required an extended amount of time to actually get into the air at the point of departure. In other words, the cost of an ‘on time’ arrival is shouldered by the passengers in the form of planned taxi delays. Our planned taxi-out time for this particular flight was 55 minutes. Actual elapsed time was 1 hour 10 minutes. So, the late departure off the gate cost an additional 15 minutes in taxi time, fuel, and passenger productivity.
On the other end of the transit to San Diego (SAN), we were instructed to descend far in advance of our optimal descent point due to conflicting traffic ahead in the Los Angeles sector. This resulted in a descent out of our 36,000 foot cruise altitude (FL360) all the way down to FL280. That’s a relatively low altitude at which to be ‘driving’ along while still 130 miles from the destination. It requires a greater specific fuel consumption rate. And it results in a slower true airspeed and a slower ground speed; the last of which directly effects arrival time for passengers. After several assigned airspeed reductions at low altitude to accommodate other arriving traffic, we touched down 24 minutes behind schedule, but didn’t get to the gate until 37 minutes behind schedule due to ramp and gate area congestion.
The takeaway:
V1 proposes that if four dimensional trajectories (4DT’s) from the departure runway to the destination final approach fix were commoditized, the cost and profit incentive would allow for a complete shift in the dynamics which determine how aircraft taxi to meet a takeoff time. As a commodity, a 4DT would be determined at the time of purchase. It would be built, bid, and transiently ‘owned’ for the optimal consumption of resources by aircraft type, forecasted meteorological conditions, and passenger and freight load. Therefore, since conflicts would be built into the price of the 4DT at the time of purchase, optimal trajectories would be immune from the vagaries of random ATC corrections for altitude, course and speed, due to conflicting traffic. This model is addressed at length in V1’s independent research proposal, The V1 Concept of Air Traffic Management.
Your comments and replies welcomed.
My best regards,
SRD
Copyright © 2009 by Scott R. Davies. All Rights Reserved.
