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Aviation Performance
Aircraft Take-Off Distance & V1/Vr Simulator
Change aircraft type, take-off weight, OAT, pressure altitude, headwind, flap setting and runway slope to see TORA, TODA, BFL and V1/Vr/V2 update in real time. Useful for High Hot Heavy performance studies, airport selection and weight-limit checks.
Parameters
Aircraft type
Sets MTOW, reference Vr and base TODR
Take-off weight
t
OAT
°C
Above ISA standard raises the density altitude
Pressure altitude
m
Airport elevation (Denver ≈ 1655 m, La Paz ≈ 4061 m)
Headwind
kt
Negative values mean tailwind (TORA grows)
Flap setting
More flap = shorter run but worse climb gradient
Runway slope
%
Positive is uphill (longer take-off run)
Results
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V1 decision speed (kts)
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Vr rotation speed (kts)
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V2 safety speed (kts)
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Take-off run TORA (m)
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Take-off distance TODA (m)
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BFL (m)
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Take-off profile — runway with V-speed markers
The aircraft accelerates past V1 and Vr and lifts off at V2. Bar lengths reflect the computed TORA and TODA.
W is take-off weight, W_ref is MTOW, ρ is air density. The take-off run scales with the square of the weight ratio, the inverse of the density ratio and the wind and flap factors.
I have seen pilots in movies shouting "V1, Vr, V2". What do those speeds mean, and are they really tied to runway length?
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Good question. V1 is the "no going back" speed — the last point at which you can abort the take-off. Past V1, even if an engine fails, you are committed to lift off because stopping in the remaining runway is more dangerous than flying. Vr is "rotate" — pull the nose up. V2 is the minimum safe climb speed with one engine out. All three depend on weight and weather, so airlines recompute them every flight in Airbus OPT or Boeing FCOM. With our default A320 at 78 t this tool gives V1 = 138, Vr = 145, V2 = 164 kts.
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Got it. If I raise the OAT slider... wow, the TORA shoots up. Why is it so sensitive?
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That is the density altitude effect. Thinner air gives less engine thrust and less lift at the same speed, so the aircraft accelerates more slowly and needs a longer roll to reach Vr. Phoenix Sky Harbor (KPHX) regularly tops 45 °C in summer, and some types like the Boeing 757 get an explicit weight limit. Denver (KDEN, 1655 m) and La Paz (SLLP, 4061 m) suffer the same problem because of elevation, even though their OAT may be mild — runway requirements there are far stricter than at sea-level Tokyo Haneda for the same aircraft.
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So when people say "High Hot Heavy" is the worst case, it is all three of those happening at the same time?
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Exactly. High elevation, hot day and heavy aircraft pile up. Regional jets like the Bombardier CRJ700 and the Embraer E190 have spent years improving short-field performance to keep flying into mountain airports under these conditions. If you push our sliders to 3000 m, 40 °C and near MTOW you will see TODA cross 4500 m and a red verdict appear. EASA CS-25 and FAA Part 25 prohibit you from departing if the required TODA exceeds the available runway at that weight.
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Flaps shorten the run, so why do pilots not always use the maximum flap setting?
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Good catch. More flap means more lift at low speed, but also more drag. The post-lift-off climb gradient drops. On a long runway with no near obstacles it is better to take off with Conf 1+F and accelerate fast; that is also easier on the engines. On short fields, or with terrain close ahead, you trade climb gradient for getting airborne early and pick Conf 3 or Full. Try switching the flap selector — Full will cut TORA by about 16 percent in this model.
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And what is the Balanced Field Length (BFL) used for?
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BFL is the runway length at which accelerate-stop (brake to a halt from V1) and accelerate-go (continue the take-off with one engine out from V1) take the same distance. If you have at least BFL of runway, anything that happens at V1 can be handled safely. That is why airport selection and dispatch planning enforce "BFL ≤ available runway length" at the chosen weight and weather. This tool shows BFL as 1.05 × TODA as a quick reference, but in real operations it is derived from detailed performance tables that include the full accelerate-stop curve.
FAQ
TORA (Take-Off Run Available) is the physical runway length on which the aircraft can roll. TODA (Take-Off Distance Available) is TORA plus the clearway, the climb segment up to the 35 ft screen height; this tool approximates it as 1.15 x TORA. BFL (Balanced Field Length) is the runway length at which accelerate-stop (decelerate to a halt from V1) and accelerate-go (continue the take-off with one engine out from V1) are equal. It is the basic indicator of runway requirement and is shown here as roughly 1.05 x TODA for quick reference.
V1 (decision speed) is the last speed at which a take-off can be aborted; above V1, the take-off must be continued even if an engine fails. Vr (rotation speed) is the speed at which the pilot begins nose rotation and scales with the square root of weight. V2 (take-off safety speed) is the minimum climb speed that guarantees a safe gradient with one engine inoperative and is about 1.13 x Vr. With the default A320 at 78 t this tool produces V1 = 138, Vr = 145, V2 = 164 kts. In airline operations the values are recomputed from weight, weather and runway by Boeing FCOM or Airbus OPT (Onboard Performance Tool) for each flight.
Performance is governed by density altitude. As air density drops, both engine thrust and wing lift fall. When the OAT is above ISA standard or the airport is high above sea level, the air thins out and the take-off run grows quickly. Phoenix Sky Harbor (KPHX) regularly exceeds 45 C in summer, forcing weight limits on aircraft such as the Boeing 757. The same effect applies to Denver (KDEN, 1655 m) and La Paz (SLLP, 4061 m); increasing the OAT or pressure altitude sliders in this tool produces a sharp rise in TORA.
Larger flap deflection raises the lift coefficient, so lift is available at lower speed and the take-off run TORA shrinks. This tool takes Conf 1+F as baseline and assumes 8 percent shorter for Conf 2, 12 percent for Conf 3 and 16 percent for Full. Larger flap also adds drag and degrades the climb gradient, so on long runways with no nearby obstacles airlines prefer Conf 1+F, while on short runways or near limit weight they switch to Conf 3 or Full as a trade-off.
Real-world Applications
Airport selection and route planning: When opening a new route, an airline computes the BFL required at the planned MTOW for every season and weather condition and compares it with the runway available at the destination. Narita 16R/34L (4000 m) is comfortable even for heavy freighters, but at La Paz El Alto (elevation 4061 m, runway 3978 m) a Boeing 737-800 sees a sharp summer weight cap. Switch between Cessna 172, A320, B777 and An-124 in this tool to see how TORA changes for the same conditions.
Operations and dispatch: Before every flight the dispatcher uses Airbus OPT (Onboard Performance Tool) or Boeing PET (Performance Engineering Tool) to compute V1, Vr, V2 and the maximum take-off weight from the day's OAT, QNH, wind and runway condition (dry / wet / contaminated). A 10 kt headwind versus a 5 kt tailwind already shortens TORA by about 22 percent in this tool.
Aircraft design and certification: EASA CS-25 and FAA Part 25 certification requires extensive flight testing and an Aircraft Flight Manual (AFM) covering the full envelope. The take-off performance charts in Boeing FCOM and Airbus FCOM are high-fidelity versions of the same weight-squared and density-altitude scaling used here. Regional jets such as the CRJ700 and E190 specifically optimise the short-field High Hot Heavy regime to access mountain and narrow airports.
Accident and performance trouble investigation: NTSB and ATSB reports on take-off overruns have repeatedly traced the cause to weight-calculation errors (actual aircraft heavier than papers), wrong OAT inputs (morning OAT applied at noon) or undeployed flaps. Playing with this tool's OAT and flap sliders builds intuition for cross-checking such numbers in the field.
Common Misconceptions & Pitfalls
The biggest trap is to treat ISA-standard performance as the operational reality. Unless explicitly noted, AFM TORA charts assume ISA, zero wind and zero slope. On a hot summer afternoon the OAT may sit at ISA+20 °C or more; in this tool, moving the OAT from 25 °C to 40 °C already lengthens TORA by 5–8 percent. On wet runways the accelerate-stop distance grows sharply and the required BFL becomes 1.2–1.5 times the dry value. This tool assumes a dry runway, so it must always be backed by the certified AFM charts for actual dispatch decisions.
The second trap is to think of V1 as a single fixed value. V1 is not just "decision speed"; it is selected within the range where accelerate-stop fits the available runway and accelerate-go is also safe. Short runways pick a lower V1 to keep margin on the stop side; long runways pick a higher V1 to favour continued take-off. Our V1 ≈ Vr × 0.95 is a rough proxy. For real operations always follow the FCOM V1 chart or OPT output.
The third trap is the assumption that "more flap is always better". More flap shortens TORA but also lowers the post-lift-off climb gradient because of added drag, which can be critical when near terrain such as around Denver or Kathmandu (VNKT). Net Take-Off Flight Path (NTOFP) clearance is tightly regulated; sometimes a larger flap setting forces a weight reduction because the OEI climb gradient becomes the binding constraint. This tool only models the TORA shortening, so climb-gradient limits must be checked separately against the AFM.
How to Use
Enter takeoff weight in tonnes (e.g., 72.5t for Boeing 737-800) and ambient temperature in °C
Set pressure altitude in meters, headwind component in knots, flap setting, and runway slope percentage
The simulator calculates V1 (decision speed), Vr (rotation speed), V2 (safety speed), TORA (takeoff run available), TODA (total distance available), and BFL (balanced field length)
Adjust parameters to analyze runway adequacy and performance margins for your departure airfield
Worked Example
Boeing 737-800 departing from London Stansted: takeoff weight 70.8t, OAT 15°C, pressure altitude 132m, 8-knot headwind, flap 5°, zero slope. Simulator outputs: V1=162 kts, Vr=169 kts, V2=177 kts, TORA=2,880m, TODA=3,060m, BFL=2,650m. The 3,200m runway provides adequate margin. Increasing OAT to 28°C raises V1 to 168 kts and TORA to 3,120m, reducing safety buffer by 80m—critical for hot-day operations at high-elevation airfields.
Practical Notes
Headwind reduces takeoff distance significantly: 10-knot headwind cuts TORA by 15–20% versus calm conditions on medium aircraft
Pressure altitude compounds hot-day penalties—a 35°C day at 2,000m elevation can increase takeoff distance 40% versus sea-level standard conditions
BFL (balanced field length) assumes engine failure at V1; runway length must exceed BFL for regulatory compliance on wet surfaces, accounting for contamination factor of 1.15–1.67
Flap setting trades acceleration for initial climb gradient; flap 5° optimizes balanced field length on most jet transports versus flap 15° for obstacle clearance