What is the ratio between time in the air and time on ground for an aircraft?

Question

I suppose it may be different from an airline to another. Given the maintenance, the time to load/unload the aircraft, the time the aircraft is grounded because there is no flight scheduled (e.g. at night), how many time an aircraft actually spend on ground compared to the time it spend in the air?

Answer 1

It will vary widely from aircraft to aircraft, but I will try to give some general estimates.

Time on the Ground

Part of what you are referring to what is sometimes called aircraft turn time. It's not really directly related to my calculations for your overall question (though it is certainly a factor for short-haul jets), but in this article, minimum turn times for the Boeing 757 was studied, and it was found that the estimated turn time for a 757-200 was 52.5 minutes, based on actual operations. The 757-300, a stretched model with more seating, would take about 59 minutes.

From this presentation, presented by United Airlines, they show a general guideline MSGT (Minimum Scheduled Ground Time), that is a generalization depending on flight locations, field facilities, and airlines. Some times are:

• Boeing 747: 80 minutes
• Boeing 777: 70 minutes
• Boeing 767: 60 minutes (-300 model)
• Boeing 737: 35 minutes (-300 model)
• Airbus A320: 40 minutes

This link has a discussion of a number of airliner turn times, however none are from official sources. Most vary between 20-45 minutes, depending on if cleaning is required.

So for a typical airliner we can say it takes about 45 minutes-1 hour for a typical servicing.

Aircraft Lifetime

Now as to how many times they fly, you can find their aircraft design cycle limit (essentially, how many takeoffs and landings it can make in its lifetime) in this Federal Register document (summarized here). Some listed numbers:

• Boeing 747: 20,000 cycles
• Boeing 777: 40,000 cycles
• Boeing 767: 50,000 cycles
• Airbus A320: 48,000 cycles (60,000 hours)
• Airbus A300: 40,000 cycles

So for a 'typical' airliner we can say it can survive about 40,000 cycles in a lifetime

You can find the average age of airliners in different places online. This site splits up by airline and aircraft, and most airliners have an average age of 12-15 years. But note that this is the active fleet. The average age at retirement for an airliner is now around 24-25 years.

You can find a related Aviation.SE question here

Aircraft Usage

This thread discusses the average cycles and flight hours per day. Long haul aircraft (like the 747, 777, A380) tend to spend more hours in the air per flight, but also have less cycles per day. I can't find official sources, but the thread presents a couple example averages for peak usage rate:

• Delta Boeing 757: 9.5 hours/4.8 cycles
• United Boeing 747: 13.2 hours/1.6 cycles

(I find these probably accurate, as there have been some publicized accidents that have much higher usage, like this one, which flew 48,740 hours and 39,781 cycles in 15 years - about 7 flights/day; short-haul jets like the one in the article end up with more cycles than long-haul, as I noted above).

It is difficult to find hard numbers, but overall, the average flight length for a short-haul jet is about 2 hours, whereas a long-haul jetliner is around 6-7 hours.

Again, there are a lot of variables in this question, but using the above data, we can estimate the answer to your question, using these estimated figures from above:

• 40,000 cycles (~20,000 flights)
• 25 years
• 2 hours/flight

This means approximately 40,000 flight hours for a typical short-haul jet; over 25 years (219,000 hours), this works out to about 1 hour in flight for every 5 on the ground. Obviously this varies widely, but for a ballpark number, that's the best I can do. The highest usage would be a heavily used long-haul jet used on the longest routes from a busy airline (i.e. trans-Pacific; Middle East to U.S.), whereas the lowest would be a moderate-length flight on a low-volume route. In general, you are probably looking at about 1:3 to 1:5 air:ground time.

Answer 2

What you're seeking is already a metric in aviation, it's called block hour.

This typically measures the time from doors closing to doors opening, so taxi time is included. Hours flown is another metric. Planestats.com parses the statistics for the US from the DOT's website, and presents it nicely (I'm unaffiliated with that website – it was a lot easier to use than to do it manually).

For the small narrow-body jets for the 12 months of 2017, the winner is 15.8 block hours / day for the A320s operated by Frontier. In second place (also A320) is JetBlue with 12.2.

So if your operation is lean and mean, you're looking at 15.8 hours a day of doors-closed and passengers on board, to 8.2 hours doing the various things you listed.

The website's summary is:

Small narrow-bodies (fewer than 150 seats) operate 9.8 hours per day while making 4.5 departures per day according to the most recent US Department of Transportation data. Large narrow-bodies (more than 150 seats) operate 10.7 hours per day and depart 3.4 times.

And for the wide-bodies:

The US wide-body fleet averages 263 seats per departure with a 4,059 mile stage length. Each plane, on average, operates 12.0 hours per day and makes 1.4 departures per day.

Taking the average of the 3 averages (three jet-liner sizes), we're looking at 1:1.22 of air:ground time.