# Tag Info

36

The other answers seem to make a simple thing way too complicated. Yes there are DMEs or TACANs, that are sometimes used to get a ground speed, but it's only accurate if you're tracking exactly to or away from it. And it certainly wasn't used to calculate speed enroute unless one of your navaids was a VOR/DME or equivalent. Rather than using DME they'd be ...

27

There is something called the "Cost Index" - it is basically how you choose between speed and fuel economy. Company dispatchers, after knowing that a flight has been delayed, will calculate this value, and the pilots simply input the updated value into the FMC (Flight Management Computer). That will instruct the autopilot to output more thrust, i.e. fly ...

23

Keeping too much speed in an approach in any airplane can be risky depending on how much runway you have as it all has to bleed off before you can stop. It's a great way to end up in a hedge. Extra airspeed means you'll either float in ground effect for a very long time, or if you somehow manage to get the wheels down you won't get much braking action as the ...

22

There are three different speeds that are of relevance here: Groundspeed- This is probably the speed indicated to the passenger. For them, this is the most relevant as it determines the time taken for the trip Airspeed- This is the speed of relevance to the flight crew and is used for flight. Local airspeed- This determines the maximum speed of (subsonic) ...

21

The brief period of leveling off is not unique to the flight on that day. Looking at track logs for previous days, it always levels off at around 7,000 feet for some period. As Terry commented, this is most likely to deal with the congested airspace. Other routes coming into and out of the London area probably pass through the same space, and keeping ...

21

Information displayed to passengers through the entertainment system often gives the aircraft ground speed rather than airspeed. Wind affects the ground speed, you're right about that. Few things out of the way first. Pilots do not use ground speed for flying, instead they use indicated airspeed. Mach number is not derived from the ground speed, as it is ...

21

There are generally two ways of determining the ground speed from within the aircraft. The first is by using an inertial navigation system. This consists of a number of accelerometers and gyroscopes that measure all accelerations and rotations of the aircraft throughout a flight. By mathematically integrating all measurements this navigation system is able ...

18

It's not so much a matter of "pilots typically get very uncomfortable" as it is "pilots recognize that it is an inherently less safe situation", and pilots (at least the ones you want to fly with) tend to be somewhat safety obsessed. So Why are tailwinds during landing "bad"? The same reason tailwinds in cruise flight are good: you're moving over the ground ...

17

There's one method that has been successfully used since long-distance flights became available - you took out your map, and tried to match it to features under your plane. This allowed you to correct your course and have an average ground speed information. Obviously, this doesn't work over the ocean - it's yet another reason why ocean flights have always ...

17

Airspeed is critical for pilots, because it is what the airplane "feels" when it's flying. Too little airspeed and the wings won't generate enough lift to fly, too much and the plane can be damaged. (And you're right, the pitot tube, along with the "static port" is what allows airspeed to be measured.) Groundspeed is how quickly you're getting where you're ...

16

You can, in theory, fly a faster landing speed than the default Vref of 1.3*Vso. But it’s wasteful in the round out and potentially very dangerous on short field landings. When an airplane lands, the pilots needs to enter the round out with only enough energy to arrest the descent and establish the airplane in the correct attitude for touchdown approx 1-2 ...

15

Looking into one set of data from the the popular Flightradar24 service it is not visible. I think I found the data you're looking at. Since the heading also suddenly changed to (exactly) 360, I'm thinking this is just an invalid data point. Notice that the receiving station jumped between these measurements and something could have happened with the ...

13

The Boeing chart you reference appears to use for the approach speed column the Vref speed of the aircraft at its max landing weight in the landing configuration. This is the speed you want to be at or close to when you start the landing flare (the two 747 carriers I flew for used Vref+5). Absent charted speed limits, controller instructions, or company ...

12

Looks like an intermediate altitude assignment from atc. A look at the standard instrument departure plates (SID's) for Stansted shows that the final altitude on some of the procedures is 6000 ft. They probably had to stay at that altitude until the departure controller passed them off to the en route controller who assigned them their cruise altitude. On ...

11

According to a story I read about the SR71, planes used to be able to ask ATC for a "ground speed check", i.e. ask "What's my speed on the ground?" ATC would measure it using their ground-based radar and relay it to the pilot by voice/radio. If you can provide some more material for us to read it would be great. Here's a video of the pilot telling the ...

11

The primary concern is the increased landing distance due to the increased ground speed. Landing & stopping distances increase more-than-linerally with each knot increase in ground speed. Given other dynamics of a landing aircraft this can be the straw that breaks the camel's back. The perfect storm True story. C-141 on approach with a tail wind - not ...

10

I'm wondering how to calculate the actual speed based on that. Which actual speed? All of the speeds you mentioned are actual speeds. None of them is in any way artificial, virtual, or otherwise invented. Is it the groundspeed plus/minus the headwind/tailwind? That would be airspeed, i.e. the speed at which the plane moves relative to the air around it. ...

10

How do head- and tailwinds affect airspeed? They don't. Airspeed is the aircraft's speed relative to the air it's travelling through. The aircraft doesn't care whether that air is moving relative to the some other object such as the ground, because the aircraft is only interacting with the air. (Similarly, when you walk to the back of the plane to go to ...

10

The higher takeoff speeds might exceed the speed rating of the usual tires. As a tire is rolling it deforms in two directions. As each section comes in contact with the runway it is pressed inward by the weight of the plane. After it leaves the runway surface the deformation is in the opposite direction from centrifugal force. This constant flexing is what ...

9

First calculate horizontal component of airspeed, then add the wind: $$v_{GS} = cos(\theta) * v_{TAS} + v_{wind}$$ with $\theta$ being the angle between the horizon and the path of the aircraft in the vertical plane. Or, if you are unfamiliar with trigonometry (using Pythagora's theorem): $$v_{GS} = \sqrt{v_{TAS}^2-v_{verticalSpeed}^2} + v_{wind}$$ Both ...

9

Course and heading are not the same. Course is the direction of your path over the ground. Heading is the direction you are pointed (and the direction you would travel through a still airmass). In your second site you entered 120 as a heading, not a course. Correct that and you get the same figures as the final site. You're doing the same thing in your ...

9

Depends. With tricycle gear airplanes the limitation is mainly pitch attitude in the landing flare so you don't come down nosewheel first, which is very bad on the nosewheel and ultimately on the airplane. So you need to be slow enough that the mains will touch first with landing flap. But beyond that it's just wear and tear on the tires and brakes. With ...

8

Basically, you're asking 'Can you achieve orbital velocity in atmospheric conditions?'. Orbital velocity is approximately equal to $$v_o \approx \sqrt{\dfrac{GM}{r}}$$ which, if we fill it in at Wolfram.alpha, yields a velocity of almost 8km/s (yes, per second), or almost 18000mph, or a Mach number of 23.23. The current speed record for sustained ...

8

It is all about the wind. If you check schedules, you'll see that for example USA-Europe flights are way shorter (about an hour, say) than Europe -USA. This is due to the jetstream. I found it even more significant in the Southern hemisphere, when flying Australia-New Zealand (and back) or Santiago-Buenos Aires. As mentioned in the other answers, no ...

7

(Source) Ground speed Ground speed equipment on-board aircraft measure the speed against the ground. Except in the case shown above where distance information is derived from a ground station (DME station). Curvature Ground speed is not derived from true airspeed. When using GPS, or an inertial navigation system to measure the ground speed, it will be ...

7

This is a very hypothetical question. If the aircraft has no means to slow down it has to lose all kinetic energy through rolling friction and air resistance. Both of these are very small (and get smaller as the aircraft gets slower) and will not have too much effect on a heavy aircraft like the A380 with an enormous amount of kinetic energy. Therefore the ...

6

Correct. True airspeed refers to the actual speed which the aircraft is moving through the air. Ground speed is the speed at which the aircraft moves over the ground. The formula $v_\text{ground} = v_\text{true} - v_\text{wind} \cdot \cos(\alpha)$ Where $v_\text{true}$ is the true airspeed $v_\text{ground}$ is the groundspeed $v_\text{wind}$ is the ...

6

How did planes measure their speed relative to the ground before GPS? Assuming you ask for speed determination by on-board instruments. The ground speed is best evaluated using an inertial navigation system. The INS knows where the aircraft is currently located (latitude, longitude, altitude). By associating two measures it's easy to compute the velocity ...

6

As others have highlighted, the question is with what ground speed you touch down. You might think that plus/minus a few knots doesn't really matter, but: your kinetic energy is quadratic in speed: E = 1/2 m v^2. if braking acceleration is constant, landing distance is quadratic in speed: s = v^2 / 2a So, to adapt voretaq7's example, if your approach air ...

5

To answer in part the question of how tailwinds are sometimes mitigated, an air carrier's op specs will typically specify how much of a tailwind is allowed for their operations. The two 747 carriers I flew for allowed a max tailwind of 10 knots. Whether a captain should choose to land given the max tailwind can be a complicated call. For example, runway 02 ...

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