Wind Correction Angle
CAS = IAS + (instrument/position correction)
TAS = CAS × √(ρ₀ / ρ) or TAS = IAS + (0.02 × IAS × Altitude(ft) / 1000)
Wind Angle = WD − TC
WCA = arcsin[(WS × sin(Wind Angle)) / TAS]
TH = TC + WCA
MH = TH − Variation
CH = MH − Deviation
In-Flight finding of Wind Speed & Direction
CAS = IAS + (instrument/position correction)
TAS = CAS × √(ρ₀ / ρ) or TAS = IAS + (0.02 × IAS × Altitude(ft) / 1000)
TH = MH + Variation
Wind Speed = √(TAS² + GS² − 2 × TAS × GS × cos(Δ))
Wind Angle = arctan[(TAS × sin(Δ)) / (GS − TAS × cos(TC − TH))]
Wind Direction = TC + Wind Angle
Takeoff / Landing / Climb Thumbrules
Practical thumb rules specifically for the Cessna 172P (180 hp, fixed-pitch prop, 1981–1986 models). These are derived from the official POH performance charts (Figures 5-5 through 5-10) and are safe approximations for sea-level to 5,000 ft density altitude, standard temperatures, max gross weight 2,400 lb, dry paved runway, no wind, flaps 10° for takeoff, full flaps for landing.
1. TAKEOFF DISTANCE (Ground Roll + 50 ft)
Thumb Rule: Takeoff distance (ft) ≈ 1,500 ft + 100 ft per 1,000 ft density altitude + 50 ft per 5°C above ISA
| Factor | Add to Base |
|---|---|
| Base (sea level, ISA, 2,400 lb) | 1,500 ft |
| +1,000 ft density altitude | +100 ft |
| +5°C above standard temp | +50 ft |
| +100 lb above 2,400 lb | +75 ft (rarely used) |
| Headwind 10 kt | –200 ft |
| Tailwind 10 kt | +400 ft |
Example:
- Density altitude: 4,000 ft
- Temp: 25°C (ISA at 4,000 ft = 7°C → +18°C → +3.6 × 50 = +180 ft)
- Calm wind Total ≈ 1,500 + 400 + 180 = 2,080 ft
2. LANDING DISTANCE (Ground Roll + 50 ft)
Thumb Rule: Landing distance (ft) ≈ 1,350 ft + 80 ft per 1,000 ft density altitude + 40 ft per 5°C above ISA
| Factor | Add to Base |
|---|---|
| Base (sea level, ISA, 2,400 lb) | 1,350 ft |
| +1,000 ft density altitude | +80 ft |
| +5°C above ISA | +40 ft |
| +100 lb | +60 ft |
| Headwind 10 kt | –150 ft |
| Tailwind 10 kt | +300 ft |
| Wet grass (short) | × 1.4 |
Example:
- Density altitude: 3,000 ft
- Temp: 30°C (ISA = 9°C → +21°C → +4.2 × 40 = +168 ft)
- 5 kt headwind (–75 ft) Total ≈ 1,350 + 240 + 168 – 75 = 1,683 ft
3. CLIMB PERFORMANCE (Rate of Climb, fpm)
Thumb Rule: ROC (fpm) ≈ 700 – 50 per 1,000 ft density altitude – 20 per 5°C above ISA – 30 per 100 lb over 2,200 lb
| Factor | Subtract |
|---|---|
| Base (sea level, ISA, 2,400 lb) | 700 fpm |
| +1,000 ft density altitude | –50 fpm |
| +5°C above ISA | –20 fpm |
| +100 lb over 2,200 lb | –30 fpm |
Example:
- Density altitude: 6,000 ft
- Temp: 20°C (ISA = –3°C → +23°C → +4.6 × 20 = –92 fpm)
- Weight: 2,400 lb (–60 fpm) ROC ≈ 700 – 300 – 92 – 60 = 248 fpm
Quick Mental Checklist (Before Every Flight)
- Density Altitude = Pressure Altitude + 120 × (OAT – ISA) (ISA = 15 – 2°C per 1,000 ft)
- Takeoff: 1,500 + 100×DA/1,000 + 50×ΔISA/5
- Landing: 1,350 + 80×DA/1,000 + 40×ΔISA/5
- Climb: 700 – 50×DA/1,000 – 20×ΔISA/5 – 30×(wt–2,200)/100
POH Reality Check
These rules are conservative approximations. Always cross-check with actual POH charts when near limits (e.g., short/obstacle fields, high DA, heavy load). Derate for engine wear and pilot proficiency.
Reality Check: At 8,000 ft DA and 30°C, takeoff can exceed 3,000 ft — plan accordingly!