Choose thrust, flap and speed together

What does the RTOM number really contain?

Performance-limited take-off mass (PLTOM) is determined by the applicable runway, climb, obstacle, brake, tyre and other performance restrictions. Regulated take-off mass (RTOM) combines the relevant limits, including the structural maximum, under the table’s definition. A table may name or code the active limit. Read the legend before interpreting it.

Keep every ceiling visible

Performance-limited take-off mass (PLTOM) is determined by the applicable runway, climb, obstacle, brake, tyre and other performance restrictions. Regulated take-off mass (RTOM) combines the relevant limits, including the structural maximum, under the table’s definition. A table may name or code the active limit. Read the legend before interpreting it.

To use RTOM data, select the actual runway/intersection, direction, configuration and aircraft variant. Enter pressure altitude, OAT and accountable wind, then apply the permitted corrections in the stated order. Read speeds at the actual take-off mass. A maximum mass and its associated speeds are not automatically today’s optimum at a lower mass.

Resolve EFB/table disagreement

An EFB can use more exact interpolation, current obstacles, different thrust/flap optimisation or more specific condition data than a printed RTOM table. That can explain a difference; it does not prove either output is valid. Compare database revision, aircraft/engine, runway start, slope, surface, packs/anti-ice, wind, units, NOTAMs and selected method before accepting the result.

A plausible mass with a wrong runway or engine variant remains wrong. Cross-check the active limitation and reasonableness, and use the operator’s approved data/process. Recompute after a material input change; do not adjust an isolated speed by intuition.

How do flex and fixed derate differ?

Assumed-temperature reduced thrust calculates a lower thrust as though the air were warmer than it is, within the approved limits. Actual OAT still governs the atmospheric and speed calculation; the assumed temperature is not substituted for actual weather everywhere. Fixed derate selects a lower certified rating, with its own performance and minimum-control-speed basis.

Two routes to less take-off thrust

Assumed-temperature reduced thrust calculates a lower thrust as though the air were warmer than it is, within the approved limits. Actual OAT still governs the atmospheric and speed calculation; the assumed temperature is not substituted for actual weather everywhere. Fixed derate selects a lower certified rating, with its own performance and minimum-control-speed basis.

Both may reduce engine wear, noise and maintenance burden while using more runway or reducing climb margin. Their permitted combination, wet/contaminated eligibility and restoration of thrust follow the specific AFM/operator method. Full thrust may be available as a response in some assumed-temperature procedures; restoring thrust above a fixed derate can invalidate a lower control-speed basis. Do not generalise across types.

Solve the temperature and the limits together

The selected assumed temperature cannot be below actual OAT and must remain within the approved assumed-temperature envelope. Find the highest approved temperature whose complete distance, speed, climb and obstacle result supports actual mass. A contamination restriction, system defect or wind condition can make the method unavailable even where the numerical runway solution exists.

Less thrust normally lengthens acceleration and can reduce climb margin. It can change the selected V1/VR/V2 schedule; these are approved outputs, not independent pilot-selected corrections. A hotter assumed temperature is not a remedy for an already climb-limited full-thrust take-off.

When can more speed produce a better climb result?

A larger take-off flap setting can lower required aerodynamic speeds and help field length, but increase drag and lower climb/obstacle mass. A smaller setting can help climb while consuming more runway. Compare the final minimum of every limit for each approved flap setting; the best individual climb mass does not automatically give the best RTOM.

Flap trades ground distance against drag

A larger take-off flap setting can lower required aerodynamic speeds and help field length, but increase drag and lower climb/obstacle mass. A smaller setting can help climb while consuming more runway. Compare the final minimum of every limit for each approved flap setting; the best individual climb mass does not automatically give the best RTOM.

An approved increased-V2 or improved-climb procedure uses extra runway and higher take-off speeds to reach a more favourable drag/excess-thrust point. It may help a climb/obstacle-limited case with spare field performance. It cannot be applied by simply adding a few knots to V2. V1, VR, VLOF, distance and the obstacle path must all be generated as one authorised case.

Ground-speed limits can end the trade

Faster lift-off raises tyre ground speed; a faster rejected take-off increases brake energy. Brake-energy limits become critical with high mass, high V1, hot initial brakes or adverse stopping conditions. Tyre limits become critical with high TAS/groundspeed from high density altitude or tailwind.

Select the option with the largest permitted final mass only after checking its full speed schedule and thrust eligibility. Where tyre or brake constraints bind, the apparent improved-climb advantage may disappear. Reducing mass, changing a valid flap/thrust option, waiting for cooler conditions or using a different runway are case-dependent remedies.

Can you make the performance decision?

Four original questions. Work from the stated conditions and review the reasoning.