Padding schedules
http://www.bbc.com/capital/story/20190405-the-secret-about-delays-airlines-dont-want-you-to-know
Your article misses many factors conducive to “padding”, or why schedule flight times have increased.
Schedules published by airlines aren’t flight times, but block times. They include taxi time out from departure gate to the runway, and from landing to the gate at destination. Actual taxi times have grown on most airport as they have spread out.
Airlines are business enterprises, so they do great efforts to improved their operations. The system is saturated, same as roads and highways. A side-effect of deregulation.
“Padding”, pertains to hub operations of major carriers and their alliance partners. It’s not intended to wilfully increase fuel burn, noise and contamination. Why would airlines do that?
Airlines are “padding” their schedules, not their actual flight times, to ensure on-time arrivals at destination gates.
They do this by statistical analysis of their actual travel times “gate-to-gate” at specific times of the day. Nothing different to what everybody does intuitively in order to arrive on-time at their job or a meeting.
Airlines increase schedule times for a substantial and economical sound objective, to ensure that their passengers don’t miss connections. Stranded passengers not only poise great demands to understaffed ground personnel, but boost costs immensely. The range goes from complimentary refreshments, meals, hotel- accommodations, to buying space on rival carriers on a higher-class. So as to reduce client legal claims.
To airlines an increase in publish schedule times has a very negative effect on their overall airplane utilisation, they need more aircraft to sustain the same route structure. Say, an airline pays 30,000 $/day for the leasing of an aircraft, it makes a difference if its able to operate six sectors a day or only five, and carry 1116 potential-pax versus 930. Imagine if you operate a significant fleet of a hundred planes.
Airlines and Airports coordinate schedules worldwide biannually, in a Symposia taking place a year ahead of the respective season. At those meetings, airport slots are exchanged and grandfather-rights defended with teeth and nails. Those agreed schedules are made available to the public and to air-traffic control agencies.
But where is the major bottleneck? Surely, runway capacity. You may squeeze so many airplanes taking-off or landing on a stretch of pavement and that varies from 30 to 60 plus movements an hour. Many factors influence that capacity, predetermined using the direction against the local prevailing winds. Other limiting factors may be the number of gates available, check-in facilities, etc.
Yet, airport operation is highly dependent on weather conditions, wind direction, visibility, thunderstorms at or around the field. Strong crosswinds may force to operate in a direction that has a single runway available, cutting capacity by half or more. De-icing or snow may wreak havoc. The ripple effect will bear upon the whole system.
Both, pilots and ATC, try hard to ensure the smoothest operation. On-time performance is a major goal. Squeezing traffic too tightly on the approach increases the chance of a go-around, if the previous aircraft hasn’t cleared the runway when the following traffic is reaching the threshold. Aircraft approach speeds vary depending on type and actual landing weight. Smaller aircraft need additional separation, if they land or take-off behind a heavy Jumbo due to vortex turbulence.
Last not least, ATC and airlines have heavily invested in ADS-B (Automatic Dependent Surveillance-Broadcast) with the goal to reduce separation. Eurocontrol is working on 4D-trajectory prediction to be able to manage flow control well in advance, spacing airplanes for approach while still in cruise.
Gazing at Jettrails 