Pete has been flying aircraft for the last 20 years. He has flown everything from light piston aircraft up to heavy jets as both First Officer and Captain. He’s currently enjoying life flying the Airbus A330 for a major international airline.
Green Dot Speed (so-called because it is displayed to the pilots as green dot on the Primary Flight Display speed tape) symbolizes the “engine-out operating speed in clean configuration” which is the speed allowing the highest climb gradient with one engine inoperative in clean configuration.
With all engines operating the Green Dot speed corresponds approximately best lift-to-drag ratio speed.
What does Green Dot Speed represent?
“Green Dot” (sometimes referenced simply as “GD”) allows the pilots at any time to instantly know what the aircraft’s best lift-to-drag ratio speed is.
Lift-to-drag ratio (also know as “L/D”) refers to the amount of lift generated by the aircraft, divided by its drag. A higher ratio means increased fuel efficiency, improved climb performance and, importantly, the best glide ratio (more on that below).
In the event of a loss of one or more engines, Green Dot represents the best Engine-out operating speed in clean configuration
On Airbus aircraft, Green Dot also corresponds to the final takeoff safety speed.
What is Green Dot Speed used for?
For enroute holding, if this is no specified speed restriction, the FMGEC will target “Maximum Endurance Speed” which equates to approximately Green Dot Speed in clean configuration. Maximum Endurance speed will vary from Green Dot to Green Dot + 10 kt approximately depending on the weight of the aircraft, its altitude and the OAT (Outside Air Temperature).
If an Expedited Climb is selected by the pilots this will be flown at Green Dot. On the “Perf Climb” page of the MCDU (Multifunction Control and Display Unit) the “EXPEDITE” field displays the time in UTC the aircraft predicts it would reach the altitude displayed on that same page.
In the event of an engine failure the pilots can reduce speed to Green Dot in order to minimize rate of descent and maximize glide range. In the event of an all engine flameout GD Speed may not displayed – in this case the crew will utilize the ALL ENG FAIL QRH procedure which includes a table of the relevant Green Dot Speed depending on altitude and aircraft weight.
Related: What happens when an aircraft runs out of fuel?
How is it Calculated?
Green Dot Speed is calculated automatically by the FAC (Flight Augmentation Computer) and is also available to pilots in the QRH (Quick Reference Handbook), in the Operational Data section which has a table showing the required speed at various weights and altitudes.
Related: What is a QRH (Quick Reference Handbook)?
Airbus A330 Green Dot Speed
- With all engines operating:
- Below 20,000 feet = 0.6 x weight in metric tons + 107 kt
- Above 20,000 feet = add 1 kt per 1000 feet
- With one or more engines outs = subtract 10 kt
As we can see from above, an increase in either weight or altitude results in an increase in Green Dot Speed.
For example, during initial climb at a weight of 200 tons (200,000kg), Green Dot Speed is approximately 227 kt (200 tons x 0.6 + 107 kt).
In the cruise at FL360 at the same weight, Green Dot increases to around 243 kt (227 + 16 kt).
If you lose an engine at the same altitude and weight, Green Dot Speed is reduced by 10 kt to give a target speed of 233kt.
Airbus A320 Green Dot Speed
Similar to the A330, the A320 Green Dot Speed can be derived from a simple forumula:
- A320 Green Dot Speed:
- Below 20,000 feet = 2 x weight in metric tons + 85 kt
- Above 20,000 feet = add 1 kt per 1000 feet
Further reading
Airbus Safety First Magazine – Control Your Speed Series
Airbus Safety First Magazine – Control Your Speed in the Cruise
Frequently Asked Questions about Green Dot Speed
What is Green Dot Speed?
Green Dot Speed is an Airbus term that symbolizes the “engine-out operating speed in clean configuration” which is the speed allowing the highest climb gradient with one engine inoperative in clean configuration and corresponds to the speed for best lift/drag ratio. Green Dot Speed gets its name from the way it is displayed to the pilots as a green dot on the speed tape of the PFD (Primary Flight Display).
What is the Maximum Endurance Speed of an Airbus?
The Maximum Endurance Speed of an Airbus corresponds to approximately Green Dot in clean configuration. It will vary from Green Dot to approximately Green Dot + 10 kt depending on the weight of the aircraft, its altitude and the OAT (Outside Air Temperature).
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Pete has been flying aircraft for the last 20 years. He has flown everything from light piston aircraft up to heavy jets as both First Officer and Captain. He’s currently enjoying life flying the Airbus A330 for a major international airline.
