Why do POH performance numbers differ from real-world performance?

POH numbers are derived from test flights with new aircraft, experienced test pilots, and optimal conditions. Real-world factors like older engines, less-than-perfect technique, and non-ideal conditions typically result in 10-20% worse performance. The FAA recommends adding safety factors to book numbers.

What safety margin should I add to takeoff distance?

The FAA recommends adding 25% to calculated takeoff distance for safety margin. For landing, add 43% to account for real-world variables. These margins account for pilot technique variations, aircraft condition, and environmental factors not captured in POH charts.

How does wind affect takeoff and landing distance?

A headwind reduces ground roll by approximately 7% for every 10% of liftoff speed as wind. Conversely, a tailwind increases distance by about 10% for every 10% of liftoff speed. This is why runway selection favoring headwind is critical, and tailwind takeoffs should generally be avoided.

How does runway surface affect performance?

Grass runways increase takeoff distance by 15-25% compared to hard surfaces. Wet pavement adds 15-20% to landing distance. Snow, slush, or standing water can increase distances dramatically - sometimes 2-3 times normal. Soft or rough surfaces also increase tire drag significantly.

What is the 70% rule for takeoff?

The 70% rule states: if you haven't reached 70% of your liftoff speed by the time you've used 50% of the runway, abort the takeoff. This provides a safety check that accounts for performance degradation. If acceleration seems slow, you'll have enough runway remaining to stop safely.

How does weight affect takeoff performance?

Increased weight requires higher liftoff speed and longer acceleration distance. A 10% increase in weight can increase takeoff distance by 20% or more. Weight also affects climb rate - critical for obstacle clearance. Always calculate performance at actual takeoff weight, not just maximum gross weight.

Aircraft Performance Factors - Takeoff & Landing Safety

Required Safety Margins

+25%

Takeoff Distance

FAA recommended margin

+43%

Landing Distance

FAA recommended margin

Book vs. Reality

POH numbers assume new aircraft, test pilots, and perfect conditions. Real-world performance is typically 10-20% worse. Always add margins.

Performance Adjustment Factors

Factor	Effect on Distance
10 kt headwind	-7% (shorter)
10 kt tailwind	+10% (longer)
Grass runway	+15-25%
Wet pavement	+15-20%
2% upslope	+10%
Each 1000 ft density altitude	+10-12%
10% over standard weight	+20%

The 70% Rule

Critical Safety Check

If you haven't achieved 70% of liftoff speed by 50% of the runway, abort the takeoff.

This rule provides a safety buffer:

Accounts for performance degradation you might not notice
Ensures sufficient remaining runway to stop safely
Works for any runway length or aircraft type
Establishes a clear abort decision point

Compound Effects

Multiple factors combine to create dramatically longer distances:

Example: "Hot and High" Scenario

Base takeoff distance: 1,500 ft

+ 5,000 ft density altitude (+50%): 2,250 ft

+ Grass runway (+20%): 2,700 ft

+ 5 kt tailwind (+5%): 2,835 ft

+ 25% safety margin: 3,544 ft required

Original 1,500 ft becomes 3,544 ft - a 136% increase!

Aircraft Performance Factors

Required Safety Margins

Performance Adjustment Factors

The 70% Rule

Compound Effects

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