How fast do planes fly? (The truth about jet aircraft)

Wondering how fast exactly planes fly? This post shares how fast various planes fly including passenger jets, military jets and cargo aircraft.

How fast do passenger jets fly?

Air speed indicator

Most jet aircraft fly at a Mach number of between Mach 0.75 and Mach 0.86. Mach number is the speed of the aircraft relative to the speed of sound. Mach 0.75 equates to 75% of the speed of sound. Similarly, Mach 0.86 refers to 86% of the speed of sound. 

Passenger jets typically cruise at between 400-550knots true airspeed. As the aircraft climbs higher, the air is less dense and there is less total drag, so the aircraft is able to fly faster.

Passenger jets typically cruise between 35,000 and 42,000ft. 400kts is the equivalent of around 460miles per hour and 550knots is equals around 630miles per hour.

How fast do planes fly - A380 cruise

Factors that affect how fast a passenger jet flies includes

  • Wind conditions
  • Cruise attitude (the higher the aircraft flies, the faster it goes)
  • Cost priority for the flight

How does wind affect how fast a passenger jet flies?

A head or tailwind will impact the ground speed of a passenger jet. A headwind will reduce the ground speed slowing the aircraft down, and a strong tailwind, with allow the aircraft to cruise at a faster ground speed, in turn flying faster.

How does altitude affect the speed of jet aircraft?

As altitude increases, so does the density of air which in turn (all things being equal) creates less air resistance or reduces drag. The reduction in drag as altitude increases is the reason that as a jet aircraft climbs, the faster it will be able to fly.

High speed f18

How does cost determine how fast a commercial jet flies?

The speed a passenger jet flies is also determined by the cost of fuel and other aircraft costs. Commercial jets do not fly as fast as they can all the time. For example, the Boeing B737-800 has a maximum cruise Mach number of M0.82 but typically cruises at between M0.75 and M0.78

It is extremely rare that a B737-800 will be flown as fast as possible in a passenger-carrying operation. The reason is that as the aircraft flies fast, a higher thrust setting is needed, which in turn requires more fuel and increases costs.

How fast a passenger jet flies is a compromise between getting to the destination at a reasonable time but also being economical in terms of fuel and engine wear. Running the engines at lower thrust settings prolongs engine life (reducing maintenance costs).

Jet engine internal

Sometimes circumstances dictate that the passenger jet is flown as fast as possible for operational reasons (e.g. the flight is severely delayed, the crew are approaching limits of their duty hours allowed for a given day – due to unforeseen circumstances like bad weather).

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How is the speed of an aircraft measured

Airspeed

Airspeed is the crucial measure that pilots use to measure their speed and which they are mostly concerned with. Wings generate lift (and allow the aircraft to fly) by air going over the wings. As a basic measurement, airspeed is how aircraft speed is measured, typically in knots

Ground speed

How fast a jet flies is affected by the wind.  Ground speed is the speed that the aircraft would travel across the ground. In still wind or zero wind, the airspeed is the same as the ground speed. A head or tailwind will either reduce or increase the actual speed travelled over the ground.

Airspeed indicator 180kts

True air speed

True airspeed takes into account change in density (due to air being less dense as the aircraft climbs), instrument error (instruments are not perfect when reading airspeed) and compressibility error.

Compressibility error is the error that happens as aircraft speed gets above roughly 300kts (345MPH) and the air ‘cannot get out of the aircraft’s way quickly enough’ so becomes compressed.

How fast does a 747 fly in MPH

The maximum operating speed of a 747 is 705.89MPH. This is Mach 0.92. Most 747’s will typically cruise between Mach 0.82 to 0.86 which equates to around 630MPH to 660MPH

Can a plane fly at 1000 mph

Planes can fly at 1000 mph. Excellent examples of planes that could fly at 1000 mph include:

  • Lockheed SR71 Blackbird (2193.2mph)
SR71 Blackbird
  • Concorde (1341mph)
  • Most supersonic fighter jets

What is the slowest a plane can fly

The slowest an aircraft can fly is the stall speed. The stall speed is the speed at which a critical angle of attack is reached – the angle between the airflow and wing incidence. Reach the critical angle of attack and the airflow over the wings starts to break down and become turbulent.

Without smooth airflow being generated over the wings, lift (that allows the aircraft to fly) is diminished and the aircraft is no longer able to fly.

A stall is when the aircraft is no longer producing lift to allow the aircraft to fly. One of the main indicators of the stall is described as the pre-stall buffet.

Airflow separating from an airfoil at a high angle of attack, as occurs at a stall.
Airflow separating from an airfoil at a high angle of attack, as occurs at a stall.
By DLR, CC-BY 3.0, CC BY 3.0 de, https://commons.wikimedia.org/w/index.php?curid=61072555

The stall speed of the aircraft depends on the weight of the aircraft. The slowest small piston engine aircraft can fly will be just above its stall speed. This can be as slow as 45knots or 52miles per hour.

In situations where there is a really strong headwind that exceeds the groundspeed, some aircraft can actually fly backwards!

Modern passenger jets typically have a stall speed of around 115kts in a landing configuration (depending on weight) which is around 132miles per hour. Flying close to the stall speed is not the safest mainly because of control difficulties.

Boeing 737 low speed landing configuration

The slowest a passenger jet will fly will be at its final approach speeds which will be around 130kts (150miles per hour).

Why do planes not fly at full speed?

Planes do not fly at full speed because it would be expensive to do so (as speed increases, more thrust is needed increasing fuel consumption and cost). The other problem with flying at full speed is that the fastest speed an aircraft can fly is normally an aerodynamic structural limit.

Fly any faster than the maximum operating speed and there is a good chance of encountering flutter, which could cause structural damage or control issues to the aircraft.

Graph of altitude/speed region envelope for Lockheed U-2 depicting coffin corner
Graph of altitude/speed region envelope for Lockheed U-2 depicting coffin corner.
By Department of Defense – AF (C)-1-1, Flight Manual, Models U-2C and U-2F aircraft. Page 6-11. Available from https://info.publicintelligence.net/USAF-U2.pdf#page=222; label added in post., Public Domain, https://commons.wikimedia.org/w/index.php?curid=87293088

Planes avoid flying too close to the maximum speed they are allowed to operate as not to exceed their aerodynamic speed limits. In smooth conditions, one can get fairly close to the maximum speed, but when conditions are turbulent it is best to leave some margin from the maximum operating speed allowed.

What is the fastest jet

The fastest jet used to be the Lockheed SR71 Blackbird (2193.2MPH or Mach 3.3).

Since the Lockheed SR71 retired, the fastest jet in the world today is the MiG-25 Foxbat (2,190mph)

Do cargo planes fly faster

Cargo planes may fly faster than commercial jets where they are carrying time-critical and commercially sensitive cargo. Typically cargo planes are variants of commercial passenger aircraft so would have similar speeds to passenger commercial aircraft. 

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Air speed indicator

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