As an aviation and vintage airliner enthusiast, I’ve watched numerous early promo films introducing new aircraft models and extolling their capabilities, some targeted at airline executives and others vying for the attention of potential passengers. ~When the first American jets entered commercial service in the late 1950s, their cruising speed of 600 mph* was highly vaunted, and would enable you to travel from L.A. to NYC, a distance of ~2450 miles, in just over four hours. In my experience such journeys usually take a lot longer. Just now we’re planning a trip to Hawaii for late in the year, and the distance is similar to the above; ~2550 miles from San Diego. For all the nonstop flights I’ve looked at departing from either SAN or LAX, flight times are just over six hours, which means the typical average speed throughout the flight doesn’t even reach 450.
So this leads me to wonder if average speeds were once faster, especially in the early days when jet flights might have been marketed as a premium service. And if so, what was the reason the airlines decided to “slow down”? One likely reason, it seems to me, could be fuel economy, especially as jet powered equipment became the ordinary standard for airlines, rather than something exotic and especially luxurious.
Or was the 600 mph figure in the early promos a sort of ideal or record speed which the airlines rarely or never have attained in their day-to-day operations?
Still another possibility is that I understand too little about the profile of a typical flight; i.e. does it take a lot longer than most people think for a plane to reach its maximum cruising altitude, and to decelerate for landing?
*Statute miles.
Airliners are designed for maximum efficiency at their cruising speed, so yeah, it basically boils down to fuel costs. Most jets can go a lot faster if they want to. I was on a flight several years ago that was delayed pretty significantly due to weather. Even though we left an hour late, we landed pretty close to on-time, so the pilot obviously punched it a bit to get us all back on schedule.
According to The Google, an A380 has a top speed of 634 mph, and a Boeing 777 has a top speed of 590 mph. For comparison, the older Boeing 707 had a top speed of 620 mph.
I am most definitely not an aeronautical engineer, but I believe that the engines on a modern jet are more than capable of pushing it to faster speeds. It’s the design of the airframe that determines the maximum speed, not engine performance. Modern jets have enough thrust that they can continue a takeoff even if they lose an engine while fully loaded. They’ve got plenty of engine power.
Modern airliners are designed for about 85 percent of the speed of sound. Once you get too close to the speed of sound, your efficiency goes to hell in a hand-basket pretty darn quickly. Those jets also aren’t designed for the aerodynamics of transonic and supersonic flight.
Back in the old days, speed and luxury were the big selling points, so I can imagine them pushing the speeds and not caring so much about efficiency. These days it’s all about cost, so they pack us in like sardines and go to much greater lengths to maximize fuel efficiency.
ETA: Again, according to The Google, a passenger jet climbs at a rate of about 1,000 to 2,000 feet per minute. So a climb to 30,000 feet would take somewhere between about 15 minutes to half an hour. I believe that the typical cruise altitude is somewhere between 30,000 and 40,000 feet for longer distance flights.
Airliners can go that fast, yes, but. Fuel alone accounts for roughly a third of an airline’s entire operating costs. The fatigue life of engine parts, and therefore maintenance costs, is closely related to maximum and maximum sustained temperatures, IOW power settings. Even on long-haul flights, higher cruise speed only shortens a flight by a matter of minutes. Even Concorde transatlantic flights eventually slowed to Mach 1.8 instead of their earlier Mach 2.2 (or something close) because it just didn’t matter to passengers. Also, some years ago the US Transportation Department put out a rule preventing flight-finder sites from ranking flights by scheduled duration, taking away the airlines’ incentive to push the throttle. So they don’t go faster than they realistically have to.
When jets were first introduced and fuel was still cheap and passengers were still enthralled by speed, airlines flying prop jobs would make a practice of pushing those big old radials as hard as they could to minimize their speed disadvantage. It was common practice, for instance, for a DC-7 captain on a New York-LA flight to stay at METO (Maximum Except Take Off) power the whole flight, and risk having to make an oil (not fuel) stop in, say, Phoenix if he figured it wrong.
I can’t easily answer what the max speeds are between older and newer jets I’m sure there are numbers on the internet but they must be taken with a grain of salt unless you have access to more detailed performance information.
I can say that in general there is a focus today on fuel economy rather than speed, so jets are certainly flown slower today than they used to be even if they are capable of going just as fast. When Boeing were contemplating the next step that became the B787 they were originally looking at a “Sonic Cruiser” that would cruise very close to the speed of sound, but the airlines didn’t want that, they wanted efficiency, and so the B787 was born. At the same time Airbus were banking on a massive hub to hub airliner (A380) which has turned out to be a misstep.
Stop reading here unless you want excessive detail.
There are some other factors in play:
If you want to go as fast as you can, you don’t go high.
The maximum operating speed (Vmo) is an indicated airspeed (IAS) at low altitudes and a percentage of the speed of sound (Mach) at high altitudes. The true airspeed (TAS) is the actual speed through the air and the TAS varies with altitude for a given IAS and Mach. The upshot of this is that when the Vmo is limited by IAS the TAS will increase with altitude and when it is limited by Mach the TAS decreases with altitude. The maximum TAS you can get is the altitude at which Vmo changes from IAS to Mach, any higher and the Vmo gives a lower TAS, and any lower and the Vmo also gives a lower TAS. This altitude varies between types but is generally in the high twenty thousands.
If you want to save fuel you do fly high, pretty much as high as you can.
You could have the very same jet with a “max speed” of 550 knots but when flying at a fuel efficient altitude, the max speed may have decreased to 500 knots.
The airspeed for best economy is generally a constant indicated airspeed regardless of altitude (there are some exceptions that aren’t worth dealing with here), and remember that true airspeed increases for a given indicated speed with increasing altitude, so the best altitude for fuel economy with the lowest impact on actual speed is as high as you can get.
It’s not all about fuel economy. An airliner’s maintenance is generally based on hours and cycles. Cycles (take-offs and landings) are constant so can be disregarded meaning that the controllable aspect of maintenance is related to airframe hours. Other factors such as crewing costs are also related to hours. The faster your jets fly, the lower the maintenance and other hourly costs will be. The slower you fly them, the lower the fuel cost will be. Somewhere in the middle is a sweet spot that gives the lowest overall cost. This will change depending on fuel prices. When fuel is cheap it may be cheaper to fly a bit faster, and when it is expensive the opposite will be true.
Airliner flight management computers/systems (FMC or FMS) have a selectable “cost index”. The company tells the pilots what cost index they want to use and the pilots enter this in to the FMS and the FMS will give recommended speeds and altitudes that achieve this cost index.
Indeed.
To give some real world numbers to my earlier paragraphs:
I fly a regional jet, it’s pretty slow compared to swept wing Boeings and Airbuses but the principles are all the same.
Its Vmo is 305 knots IAS up to about 24500 feet where it changes to a limit of Mach 0.72 (24500’ is where Mach 0.72 = 305 knots IAS).
Its max altitude is 35000’ and its best speed for economy is around 250 knots IAS regardless of altitude (speed for economy is indicated speed, not true speed).
If we wanted the fastest true airspeed we would fly at 24500’ and we could do about 435 knots, call it 425 knots because you don’t want to have an overspeed. At the same altitude, the best economy speed would be around 360 knots TAS, a big difference.
At 35000’ however, the max speed has dropped to 415 knots, but the associated indicated airspeed is 240 knots. So the indicated speed has actually dropped slightly below the best economy speed. At 35000’ max speed and best economy are in effect the same speed, 405 knots TAS (allowing for a 10 knots buffer on the Vmo again). So we always fly at 35000’ right, because we can go 45 knots faster for the same economy? Well no, often we are too heavy to get up there or the sector is too short. If we are flying 150 miles, we aren’t climbing much higher than 24000’.
So what is the cruise speed? Answer, there is no one cruise speed, it all depends on a range of factors and numbers presented in wikipedia articles and on manufacturer’s websites are a bit meaningless by themselves.
This is another big factor. Jetstreams can be well in excess of 100 knots. Flying at a TAS of 450 knots could give a ground speed of 600 knots flying east and 300 knots flying west.
Altitudes have increased …
So it turns out they go more efficiently at higher altitudes, but the trafe off is that if there is a headwind, then its a slow down.
So going an hour faster due to bad weather may be due to either flying inefficienty, OR because the flight time had no headwind to contend with… or both… among other factors. (is the flight time stated as one hour longer than it would take due to the frequency of delays ?)
The speeds (‘full size’ jet) airliners are capable of has basically leveled off in the past 50 years. Fig 28 on article page 652 (.pdf pg. 24) of this link has an interesting graph comparing to the preceding years. It’s a scatter plot with some modern airliners having cruise speeds below the standard set by the 707, others slightly above, and not every plane so far mentioned in the thread is in the graph which is also from almost 20 yrs ago. But the general trend remains today: no strong trend in either direction in airliner cruiser speeds. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.539.1597&rep=rep1&type=pdf
Aerodynamic advancements of that period would allow at least slightly higher cruise speeds if designers chose them, for example by virtue of supercritical wing sections as noted on that graph. Those sections delay the onset the Mach drag rise and allow a
slightly higher cruise speed all else equal. But designers have instead focused on fuel efficiency in aerodynamic design (even besides improvements in engines).
An exception recently is commercial projects seeking to create economically viable supersonic airliners. But they aim to fill a market niche if they can profit at ticket prices in the same price range as first class on regular airliners, IOW way above normal economy class fares: they don’t aim to replace subsonic airliners.
Aeiron and Boom are two examples: https://www.aerionsupersonic.com/
Also the Cessna Citation X though not an airliner is an example of applying recent decades’ advances toward higher subsonic cruise speed in a basically conventional a/c (the faster Sonic Cruiser at least in artists’ depictions would have featured a radical configuration). Its max cruise is 978 km/hr (somewhat above the trend line in fig 28) v 903 km/hr for 787. http://cessna.txtav.com/en/citation/x#specs
I read that airlines consider being on time more important than being fast. Suppose you have an airplane which is capable of getting from Point A to Point B in 4 hours. You could schedule takeoff at 11 am and landing at 3 pm. But what if the takeoff is delayed an hour due to congestion at the airport? Then you land at 4 pm and some of your passengers miss their connecting flights. You have more options if you schedule the takeoff for 10 am. If the takeoff is on time, fly from Point A to Point B at 80% speed, save fuel, and get there right when you promised. But if the takeoff is an hour late, fly at max speed, burn the extra fuel, and still get there on time.
According to this article, airlines schedules have gotten more and more pessimistic in the last two decades, in order to artificially inflate their On-Time Performance. But the airlines deny it. They say the schedules are based on past performance. But logically, if you’ve been intentionally flying the plane slower to save fuel and then you base your schedule on that history, then it amounts to the same thing. You’re scheduling the flights based on the assumption that you will probably fly slower to save fuel, just like you always do. But if you’re delayed, you can “make up some time in the air”.
This is surprising. With regard to the non-safety-related aspects of commercial aviation, like fares and marketing, I thought the airlines and their agents could do pretty much as they please.
Getting to my destination a half-hour sooner doesn’t really matter to me; I’m just curious about these things. I understand a lot of people hate to fly or are fearful of flying, and for them a flight can’t end soon enough. But I’m mostly OK with it.
If cheap airfares and economy passengers hadn’t actually mattered, airlines wouldn’t have forced their first-class passengers to use the 747 instead of the Concorde.
There weren’t enough first class passengers to pay for both the 747 and the Concorde. The Concorde was too expensive to keep operating only after the decision to fly the 747.
707s weren’t routinely being flown from Los Angeles to NYC in four hours. I looked at an old American Airlines schedule and they booked the flights at 5:15.
Missed the edit window: And I just checked the last five LAX-JFK flights on FlightAware, which shows the actual time in the air, and they made the trip in 5:20, 5:21, 5:27, 5:33, and 5:17. That’s a little slower when you add in the ground time (which wouldn’t have been as much in 1961 since airports weren’t as busy) but not all that much.
There’s nothing wrong with that though. It’s not a win/win for the airline to have slower schedules, if they’re too slow then they can’t fly as many sectors per day. It is in everyone’s best interests for the schedule to be realistic. That a realistic schedule allows for an on time flight to fly slow and save fuel and a late flight a bit of buffer to make the schedule isn’t some kind of nefarious scheme, it’s just a side effect of the fact that fuel economy has become king and so the slow on-time flight is what the schedule is designed for.
In the US, airlines are scored and reported by the DOT for their on-time performance. That gives them an incentive to pad the schedules a bit.
Also, since a departure officially occurs when the door is closed, they have an incentive to do so on time and turn away late-arriving passengers, even if the plane is going to have to just sit there for awhile for some reason.
Also, some airports have noise reduction agreements that limit the number of departures scheduled between midnight and 6am. So you will see a lot of them scheduled for the last 15 minutes before midnight, possibly even more than the airport runways can handle. As long as the aircraft door is closed by then, on paper, they appear to have met those noise reduction agreements, even if the plane waits a while before actually taking off.
According to some internet site I don’t remember, another reason for lower cruising speeds in modern jets is that the high bypass engines now used are most efficient at slightly lower air speeds than older engines with lower bypass ratios.
