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In the Airbus brochure (more like a book) Getting to Grips with Aircraft Performance, the standard climb profile for the A320 family is mentioned as

250 kt / 300 kt / M0.78

With this accompanying chart:

Climb profile showing crossover

(image taken from Getting to Grips with Aircraft Performance by Airbus)

So these speeds (the first two phases) are certainly IAS.

The book mentions the reason for the initial 250 kt to be due to ATC restrictions <10k ft. I ran a search and found this to be true.

However, very ironically, this website (eurocontrol.int), gives the following figures:

290 kt / 290 kt / M0.79

Eurocontrol's performance chart for A320

(image taken from eurocontrol.int)

As visible from the chart, even this source clearly states that the speeds are in IAS.

TL;DR

Can someone reconcile this conflict: How can eurocontrol.int claim that the A320 flies at 290 kt under 10k ft, with Airbus's own book claiming otherwise, and why do these sources differ (250/300/0.78 vs 290/290/0.79) ? Which profile is more accurate to what real pilots fly?

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The first profile you show is a typical climb profile for the A320. You have the usual 250 KIAS constraint below 10,000 ft and then climb at 300 KIAS until reaching the climb Mach of 0.78. The exact values of 300 and 0.78 will however differ for every flight. These are just typical values.

The optimal climb speed and mach number is determined by the FMGC (Flight Management and Guidance Computer) on the A320:

The FMGC computes optimum speeds, based on:

  • Gross weight (GW)
  • Cost index (CI)
  • Cruise flight level (CRZ FL)
  • Wind and temperature models
  • Performance factor

When there is no time or speed constraint/limit, ECON SPEED is the optimum speed for the selected cost index. It refers to fuel and time cost, and not directly to fuel saving. The FM calculates ECON CLB, ECON DES and the associated top of climb and top of descent as a function of cost index, cruise FL, and meteo data.

(Airbus A320 FCOM - Autoflight - Flight Management)

The primary way to influence these speeds is by selecting a different cost index. The cost index to choose is usually selected by the airline. A lower cost index results in less fuel burn, but longer flight time, and vice versa.

The second profile you show is from the Eurocontrol performance database. This is information for air traffic control and planning purposes that shows the aircraft's capabilities at typical weights. This just means the A320 is capable at climbing at 290 KIAS (even below 10,000 ft) until reaching Mach 0.79. Note that the page then also shows the climb rate that can be achieved at these speeds, which is helpful for anticipating possible future conflicts with other aircraft. The actual profile flown can however differ from this one. Climbing at lower speeds would then result in higher climb rates and vice versa.

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The 250kt speed limit below 10'000 is not universal. It depends on the airspace class and country-specific rules what the exact limits are.

The Airbus manual has provided a climb profile for the lowest common denominator, which is climb with the speed limit imposed. In theory one could execute that climb profile in any jurisdiction.

The Eurocontrol manual is specific to the situation in most EASA countries, where speed limits are different. For example, while in the US class A airspace is never below 18'000, around Amsterdam Schiphol airport the class A starts at 1'500, and a high speed climb is preferred. See What is the speed limit in European airspace? for more information about speed limits in EASA-land.

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  • $\begingroup$ "a high speed climb is preferred" -> are you sure? Even if it is in class A airspace, every SID chart of Amsterdam contains this speed constraint: "SPEED: MAX 250 KT BELOW FL100 UNLESS OTHERWISE INSTRUCTED". $\endgroup$
    – Bianfable
    Jun 12, 2021 at 8:38
  • $\begingroup$ @Bianfable The "otherwise instructed" is pretty much the norm. Departure typically approves high speed climb on initial contact. $\endgroup$
    – Sanchises
    Jun 12, 2021 at 9:07

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