Hot and High: Why Aircraft Lose Range at Denver and La Paz
Engine thrust and wing lift both depend on the density of the air the airframe moves through. At sea level density is the reference. At Denver it is about 14% lower. At La Paz Bolivia it is 40% lower. The result is a real, year-round payload-range constraint that every aircraft type sees and every published flight manual quantifies.
The Physics
A turbofan generates thrust by accelerating a mass flow of air. Less dense air means less mass flow at the same compressor speed, which means less thrust. A wing generates lift by deflecting air at speed; less dense air means less lift per knot of indicated airspeed. At higher elevations the airframe needs more runway, lifts off heavier slower, and climbs out shallower.
Aircraft manufacturers publish performance-limited takeoff weight charts in their approved flight manuals. Great Circle Pro's planning model uses that same idea at map scale: Denver lands near a 4% range reduction in the model, while a very high field such as La Paz is closer to the low-20% range. Treat those as planning-envelope examples, not universal dispatch limits for every aircraft, runway, temperature, and payload.
The Math We Use
Great Circle Pro models this as a linear elevation derate, calibrated against Boeing AFM and Airbus PLTOW: about 2.2% range loss per 1,000 ft above a 3,500 ft threshold, floored at 45%. Worked numbers from the 19-airport list:
- Denver KDEN, 5,431 ft → 4.3% range loss
- Mexico City MMMX, 7,341 ft → 8.4%
- Bogotá SKBO, 8,361 ft → 10.7%
- Cuzco SPZO, 10,860 ft → 16.2%
- La Paz SLLP, 13,313 ft → 21.6%
The derate is applied to the published range, then to the wind-adjusted range, then to the range-exceeded check. Range circles drawn from a hot-high origin contract proportionally.
Year-Round
Pressure altitude dominates at the airports we cover. La Paz at 13,313 ft is thin air even on the coldest Bolivian winter morning. Denver's January air is denser than its July air, but still meaningfully thinner than sea level. The planning-fidelity baseline applies the full elevation derate every season as a conservative default; seasonal modulation of the "hot" component is a possible future refinement.
Try it. Plot a Denver or La Paz departure with the Hot-high toggle on, then off. The block-time gap, the range-exceeded badge, and the range-circle contraction all reflect a real-world MTOW constraint that operators dispatch against every day.