When different people talk about how long their flight is, they might mean different things.
Some might say “I’m taking a 20-hour flight to Japan” and include two flights and a transfer time in their calculation. Others might say “it’s a 12-hour flight” and mean just the actual flying time – i.e. the time their aircraft is airborne. And, some might say “my flight’s 13 hours” and mean the actual scheduled flight duration.
In this article, I will look at a couple of different ways flight duration can be defined including block time, flight time, and airborne time. I will also look at what affects them.
Block Time vs. Flight Time vs. Airborne Time: What Are the Differences?
When it comes to measuring flight duration, there are a couple of different ways one can do so, each used for a different purpose.
First, there is block time. This is what you will find in airline schedules and on your ticket when you book a flight. Block time starts when an aircraft goes “off blocks” – i.e. when chocks are removed by ground staff and the aircraft starts being pushed back. It ends when an aircraft is “in blocks” – i.e. comes to a full stop at its arrival gate – at its destination. In other words, it is the duration between a flight’s departure time and its arrival time.
Because of this, block time includes not only the time the aircraft spends in the air but also the times it takes to push back and taxi to and from the departure and arrival runways respectively.
As for flight time, there are two possible meanings.
In the United States, the Code of Federal Regulations (CFR) defines flight time for powered aircraft as “pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing.” It is used for setting restrictions on how much flight time pilots can log in a certain time window.
When defined this way, flight time is essentially block time excluding push back time and the time it takes to get the engines started and start taxiing out. That said, in irregular operations, things get a bit more complex as flight time could actually encompass two flights when a flight diverts and then continues on to its actual destination. If you are interested in the details, you might find reading the FAA’s analysis of a couple of such scenarios interesting.
More generally, flight time is used to refer to airborne time. In this case, it is the duration between a flight’s take-off time and landing time. When a flight attendant on your next flight announces “our expected flight time today is 2 hours and 40 minutes,” this is what he or she is referring to.
5 Things That Affect Flight Duration and Scheduling
Largely speaking, there are five things that airlines take into account when determining flight schedules and that affect flight duration. While the first two only affect block time and flight time as defined by the CFR as they are ground movement-related, the remaining three affect airborne time too.
The below also explains why two flights on the exact same route can show up as having different duration when you search for your flights.
Departure and Arrival Airports
When determining flight schedules, one of the factors airlines need to take into account is the route – i.e. which airport a flight departs from and which airport it arrives at.
That’s because flying into and out of different airports, airlines can expect their aircraft to spend different times on the ground trying to make their way to the departure runway or arrival gate and in the air waiting for their turn to land. Things like airspace and airport congestion need to be taken into account but so does the layout.
While getting pushed back and taxiing to the departure runway might be a matter of ten or fifteen minutes at a small regional airport, it might take many times longer at an airport like New York JFK where dozens of aircraft tend to be waiting for departure during busy periods of the day or like Amsterdam where one of the runways (Polderbaan) is a very long taxi away from the terminal.
As an example, my most recent flight out of JFK airport was pushed back seven minutes ahead of schedule. From there, however, it took exactly an hour until it was our turn to take off. While we ended up arriving in Vienna late, we were only 19 minutes behind schedule as opposed to the full hour because, to an extent, the airline was expecting the long take-off queue.
Departure and Arrival Times
Related to the above but more specific to congestion, availability of gates, and similar factors, block time also depends on the scheduled departure and arrival time of the day. That’s because some airports can be busy at certain times of the day (morning departure bank, for example) while they may be less congested at other times of the day (mid-day at some airports, for example).
As such, there can be cases where the same airline operating the same route with the same aircraft type schedules individual rotations at different durations.
One likely example of such case is Emirates’ Dubai – Jeddah route. The airline currently operates three daily rotations on the route with each having a different scheduled flight duration. The flight departing Dubai at midnight has a scheduled duration of 1 hour and 55 minutes, the one departing in the early morning of 2 hours and 5 minutes, and the one departing in the late afternoon of 2 hours and 10 minutes.
No doubt this is the most obvious of the factors. The further apart the two airports between which a flight operates are, the longer the flight is going to take if all other things are equal. Flying from Frankfurt to Paris is going to take much less time than flying from London to New York.
That said, it’s important to keep in mind that while when giving you miles, airlines use the great circle distance (i.e. the shortest distance between your departure and arrival airports), when calculating flight times, they need to consider the actual flight route. While this might be roughly the same as the great circle route, it might also be considerably different.
Some of the reasons it might differ include air currents (in that case, the increase in distance is offset by the increase in ground speed thanks to tailwind) and geopolitical circumstances (in that case, like with the Russian airspace not being accessible to many airlines right now, the flight simply becomes longer).
Air Currents and Season
Speaking of air currents, they need to be accounted for when planning block times as well. After all, “we were encountering some headwind” when one can always expect a headwind in that direction is not an excuse for a flight being delayed and potentially having a knock-on effect on other flights.
The effect of this can be seen when looking at the scheduled durations of flights flying in the east-west and vice versa direction. You will generally notice that flights flying westward between the same pair of airports are shorter. One specific example is flights between Japan and the Middle East – Qatar Airways flight from Tokyo to Doha is currently scheduled at 13 hours and 5 minutes while its flight from Doha to Tokyo is just 9 hours and 55 minutes.
With some air currents varying depending on the time of the year, the season during which a flight takes place needs to be accounted for as well.
While there are slight differences, the cruising speeds of modern jet airliners are fairly similar across different types. That said, the cruising speeds of turboprops and jets can vary significantly.
Because of this, a flight operated by, let’s say, a Boeing 737 might have a slightly shorter block time than the same flight operated by, let’s say, an ATR 72.
Lastly, in addition to the above, airlines also have their own preferences when it comes to how much to “pad” their schedules to accommodate for any unexpected delays. While some airlines might prefer to set their scheduled flight duration shorter to appear as the faster option in search engines, others might prefer to set the duration longer to improve their on-time performance.
After all, a flight being on-time is relative to the block of time that passengers and the airline scheduled the flight to take. If two flights with different block times depart the same airport at the same time and arrive at the same airport at the same time, there is a chance that one will be late and the other one early.
If you happen to be on the “early” one and fly on Ryanair, you might even be able to enjoy the airline’s “we arrived on time” fanfare…
Scheduled vs. Actual Block Time
One last thing to note is that, naturally, there is – more often than not – a difference between a flight’s scheduled block time and its actual block time.
This can be for many reasons including weather (headwind or tailwind being stronger or weaker than assumed in the scheduled block time calculation), longer than usual taxi time, different than expected runway being at use at the arrival airport and thus longer flying time being required, and so on.
While block time is the full length of the flight including the time it takes the aircraft to get to the departure runway after starting to move and to get to the arrival gate after landing, airborne time (or flight time in most cases) take into account only the time the aircraft is actually flying.
As such, when making plans – whether you making your schedule for the day or an airline planning its operations – block time is the one to be taking into account.