Definition
ECON speed is an economy cruise speed calculated by the flight management system (FMS) that balances fuel cost against time cost to produce the most cost-effective speed for a given flight. It is derived using a cost index entered by the operator, which weighs the value of time relative to the value of fuel.
Plain English
The speed the aircraft's computer works out to give the cheapest overall flight, taking into account both how much fuel costs and how much time costs the airline.
Context Anchor
Seen on flight management system pages and in VNAV planning, especially when the aircraft is calculating climb, cruise, or descent speeds.
Derivation
Short for 'economy speed.' The term comes from the idea of an economical cruise — not the slowest, not the fastest, but the speed that costs the operator the least overall once fuel and time are both priced in.
Why Pilots Care
Using ECON speed reduces fuel consumption and operating costs without extending flight time beyond the airline's chosen cost index.
Intuition Check
ECON speed does not mean the slowest possible speed. It means the system’s calculated best tradeoff between fuel, time, and performance for the current settings.
Example Sentence 1
After level-off at FL370, the crew selected ECON speed on the FMS and let the autothrottle manage the cruise.
Example Sentence 2
As the aircraft began VNAV descent, the speed target changed from ECON to a lower value for the approach.