Uphill Runway, High Density Altitude, and the Rejected Takeoff
You are planning a departure from a 1,600 m paved runway at elevation 1,450 m. OAT is 28 °C, QNH 1005 hPa, and the runway has a 1.2% uphill slope in the takeoff direction. Aircraft mass is 300 kg below MTOM. The AFM gives, for these conditions, a takeoff distance to 50 ft of 1,380 m and an accelerate-stop distance of 1,520 m, both on a level, dry runway at sea-level reference conditions, already corrected for the reported temperature and pressure altitude. The runway is dry. The first officer notes that 1,380 m is less than 1,600 m and suggests the takeoff is legal.
1. Evaluate whether the takeoff distance to 50 ft is acceptable, accounting for the slope and the regulatory margin.
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Two corrections must be applied to the 1,380 m figure before comparing with 1,600 m.
1. Slope. A 1.2% uphill slope increases takeoff distance. Using a typical AFM gradient of about 5–6% additional distance per 1% uphill, the penalty is roughly 1.2 × 5.5% ≈ 6.6%, i.e. about +90 m. Corrected TOD ≈ 1,470 m.
2. Regulatory margin. Under the applicable performance rules, the takeoff distance available must be at least 1.15 × the TOD to 50 ft (for a dry runway). 1.15 × 1,470 ≈ 1,690 m.
1,690 m exceeds the 1,600 m available. So the takeoff is not legal on TOD grounds, even though the raw 1,380 m is less than 1,600 m. The first officer compared an uncorrected, un-margined figure with the runway length - that is the error.
The 300 kg below MTOM does not fix this by itself; you would need to reduce mass enough that the corrected, margined distance falls below 1,600 m, or change runway/conditions.
2. Now check the accelerate-stop distance and state what it tells you about the takeoff.
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The accelerate-stop distance of 1,520 m is the distance to accelerate to V1, recognise a failure, and stop - again on a level dry runway. Apply the slope correction: 1.2% uphill reduces the stopping distance slightly (you are stopping uphill), but the acceleration phase is penalised; conservatively treat the net as neutral to slightly adverse and use ≈1,520 m.
The regulatory requirement is that the accelerate-stop distance must not exceed the runway length available (i.e. 1,600 m). 1,520 m < 1,600 m, so ASD is satisfied with about 80 m to spare.
The combined picture: ASD is fine, TOD is not. That means you cannot simply reduce V1 to shorten ASD - ASD is already the comfortable one. The binding constraint is the all-engines takeoff distance, so the fix is to reduce mass (or wait for cooler conditions / use another runway). Reducing mass shortens TOD; it does not help ASD much, but ASD is not the problem.
3. What operational decision do you make, and how do you brief it?
Read the worked answer
Decision: do not depart at this mass from this runway in these conditions. The corrected TOD (≈1,690 m required) exceeds the 1,600 m available. Options, in order of preference:
- Reduce mass - offload fuel or payload until the corrected, 1.15-margined TOD is below 1,600 m. Recompute with the AFM, do not estimate.
- Wait for cooler conditions - the afternoon temperature peak is the driver; a later departure or early morning reduces density altitude.
- Different runway or airport - a longer or downhill runway, or a lower-elevation field.
Brief to the crew: the binding limit is takeoff distance, not accelerate-stop; V1 is not the lever. State the new mass, the recomputed TOD with slope and the 1.15 factor, and confirm the ASDA still covers the accelerate-stop distance. If any doubt remains, do not go - a rejected takeoff uphill at high density altitude is the worst case you can put yourself in.