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I came across this page where a DC-8 set a record in 1964 for a 12h24m flight from Montreal to Tokyo. Last year I flew to Tokyo from Montreal and it took 9h from Vancouver (where I had a layover)

I suspect the answer is along the lines of "for safety reasons", but surely in the 5 decades since that record airplane design and safety protocols have improved such that today's planes can fly faster and safer.

Am I mistaken in that airlines today don't fly at the fastest the airplanes can ? If so why not ?

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  • $\begingroup$ @ymb1 5h to Vancouver then 9 to Tokyo, Air Canada has a direct Toronto-Tokyo that still takes 15h I think $\endgroup$
    – user16108
    Sep 9, 2016 at 12:48
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    $\begingroup$ I would like to add that there is not much speed difference in maximum between older and new jet airliners. They are all within a 40 knot variation around 480 or so knots. $\endgroup$
    – SMS von der Tann
    Sep 9, 2016 at 12:49
  • $\begingroup$ @ymb1 wait what ? :p 9+5=14 not counting the 3h layover in Vancouver $\endgroup$
    – user16108
    Sep 9, 2016 at 12:58
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    $\begingroup$ It has nothing to do with safety, and everything to do with economy. $\endgroup$
    – abelenky
    Sep 9, 2016 at 13:53
  • $\begingroup$ A 737 can fly 583 mph. The distance from Boston to Cleveland is 640 miles, so if this aircraft was operated at top speed (and, of course, not allowing for takeoff, climb to altitude, descent, or landing, because what would the fun of that be? :-) it should be able to make the trip in about an hour and 6 minutes. So why do my daughter's flights back and forth take about an hour and 45 minutes? Dang it! I want someone to blame, and I want them NOW!!!!! :-) $\endgroup$
    – Bob Jarvis - Слава Україні
    Jun 24, 2017 at 20:53

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The key issue that determines the aircraft speed is economics. Airlines fly the aircraft that make most sense economically- which is rarely, if ever, the fastest speed possible (more speed equals more drag usually, which reduces fuel economy). More fuel efficient the aircraft is, better the range/passenger capacity, making airlines more money.

The top speed of the (subsonic) aircraft has changed only a little in the past few decades- most developments have been geared up towards improving fuel efficiency, not increasing speed (speed alone doesn't make economic sense to airlines; look at what happened to Concorde).

There is another issue here- most of the passenger aircraft fly in high subsonic (transonic) regime. As a result, the airliners are flown below the drag divergence mach number, beyond which the drag increases rapidly. This limits the aircraft speed.

As a related point, due to the high altitudes at which the aircraft are flown is that there is little speed range to chose from between the stall speed (lowest speed possible) and critical mach number (highest speed possible beyond which flow separates due to local supersonic flow). This limits the practical options available to the pilot.

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It costs lots of fuel, and hence money.

Drag scales with the square of velocity, and you have to overcome drag with thrust. Moreover, currently airliners fly just below the transonic range, where the drag increases much faster.

In addition, to carry the extra fuel that is needed to be faster towards the end of the journey, you have to carry additional extra fuel during the early portion of the flight.

Are you willing to pay for all that extra fuel, just to slightly reduce the flight time? Are there enough people that want to pay that and can afford it, so that the airliners will not fly empty?

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The record was set on the return flight. This will be faster as the plane will be flying in tailwind, increasing its ground speed.

Nowadays Tokyo to Vancouver (7h57) plus Vancouver to Montreal (4h11) totals 12h8m, it beats the record despite having to take off twice, change to a slower plane, and fly at least 430 NM more than a direct flight.

enter image description here
(gcmap.com)

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  • $\begingroup$ Thanks, I guess I was counting gate to gate maybe ? Anyway, the flight I took back was 8h20 on average, AC4 $\endgroup$
    – user16108
    Sep 9, 2016 at 13:54
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We've previously had this discussion with the reason Concorde is no longer in service. The basics: Design complexity increases with speed and heat, driving up costs. Government regulators won't allow for supersonic flight over land, engine efficiency limits range to approximately 4000 NM, so Pacific routes are limited and all SSTs (Super Sonic Transports) so far have been commercial disasters requiring considerable government subsidies to keep them operational.

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