FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsEasy
A dispatcher plans a flight at Mach 0.80 (480 KTAS) eastbound through a jet stream core with a 150-knot tailwind component. What groundspeed should the crew expect while in the core, and what is the primary planning implication?
- A630 knots groundspeed; but fuel burn increases due to headwind drag
- B330 knots groundspeed; longer flight time and higher fuel burn
- C480 knots groundspeed; the jet stream has no effect on groundspeed
- D630 knots groundspeed; shorter flight time and fuel savings
Show answer & explanationAnswer & explanation
Correct answer: D. 630 knots groundspeed; shorter flight time and fuel savings
Groundspeed = TAS + tailwind component = 480 + 150 = 630 knots. A strong tailwind in the jet stream core increases groundspeed, shortening flight time and typically reducing fuel burn for that segment, which is why eastbound flights often route to take advantage of the jet stream.
Why the other options are wrong
- A. Contradicts the given tailwind; headwind drag doesn't apply here.
- B. This describes a headwind scenario, not a tailwind.
- C. The jet stream directly changes groundspeed via wind component.
Jet Stream & TAS/Groundspeed
Jet streams are narrow high-altitude wind bands (often 100+ knots) that add to or subtract from TAS to produce groundspeed, greatly affecting flight time and fuel planning.
- Jet stream winds can exceed 150-200 knots
- Groundspeed = TAS ± wind component
- Eastbound flights often seek jet stream tailwinds; westbound flights avoid them
Memory trick: Ride the river of wind eastbound