Declared Distances: TORA, TODA, ASDA and LDA

A runway is more than a strip of pavement of known length. For each direction of use, the aerodrome declares how much runway is available for the takeoff run, how far an airplane may travel before it must reach its screen height, how much ground there is to accelerate and then stop, and how much runway lies beyond the threshold for landing. These four figures are the declared distances: TORA, TODA, ASDA and LDA. They are published in the AIP, they often differ between the two directions of one runway, and they can be shorter than the pavement itself.

Declared distances are the "available" half of every runway performance calculation: the flight manual gives the distances the airplane requires, the AIP the distances the runway offers, and the operating rules say how the two must compare. Read correctly, the four figures show at a glance whether a runway has a clearway, a stopway or a displaced threshold. The required side is covered in takeoff distances and field length and landing distance.

What declared distances are

The definitions come from ICAO Annex 14, Aerodromes, Volume I, and are used in the same form by EASA and, with minor differences, by the FAA.

Some textbooks and exam questions phrase TORA as the distance from the point where the takeoff run can begin to the nearest point where the surface can no longer bear the airplane's mass, and some call the ASDA by its older name, the emergency distance available (EDA).

Two points follow from the word "declared". The figures belong to a runway direction, not to a runway: runways 05 and 23 of the same pavement each have their own set. And they state what the aerodrome declares suitable, not what is painted: it may declare less than the physical length to keep a safety area beyond the runway end, to clear an obstacle or during works, and performance is then based on the declared figure.

TORA and TODA

TORA normally covers the whole runway in that direction, from where the takeoff run can begin to the end of the pavement able to bear the airplane. TODA adds the clearway.

A clearway is a defined rectangular area, on the ground or on water, under the control of the aerodrome authority, over which an airplane may make part of its initial climb. Under Annex 14 it begins at the end of TORA, extends at least 75 m either side of the extended runway centerline and should not be longer than half of TORA, so TODA can never exceed 1.5 times TORA. The FAA's definition in 14 CFR Part 1 asks for a width of at least 500 ft and expresses the clearway as a plane rising from the end of the runway at no more than 1.25 percent, above which no object or terrain may protrude.

A clearway need not be paved or strong enough to carry an airplane, which is already airborne over it, so it counts only toward TODA. The Performance Class A takeoff run required, which must fit within TORA, ends midway between lift-off and the 35 ft screen, so at least half of the airborne distance is flown over the runway itself. At Nice, runway 04R has a TORA of 2,963 m and a TODA of 3,503 m: a 540 m clearway beyond its north-east end. French visual approach charts draw a clearway as a dashed rectangle beyond the runway end and a stopway with a solid outline.

ASDA and stopways

ASDA is TORA plus the stopway. A stopway is a defined rectangular area at the end of TORA, prepared as a suitable area in which an airplane can be stopped after an abandoned takeoff. It is as wide as the runway and must be able to carry the airplane without structural damage, but it is not used for the takeoff run or for landing. It lies within the runway strip, and where it is used at night it carries fixed, unidirectional red stopway lights showing toward the runway. The FAA marks stopways and blast pads with yellow chevrons, and they may not be used for taxiing, takeoff or landing.

Strasbourg Entzheim shows both features on one runway. Runway 05 is 2,400 m long, with a 270 m concrete stopway and a 295 m clearway beyond its end, so its TORA and LDA are 2,400 m, its ASDA 2,670 m and its TODA 2,695 m.

Pavement beyond the runway end counts only if the AIP declares it as a stopway, which Nice, for example, does not do for the chevron-marked area beyond runway 04R.

When ASDA equals TODA the field is balanced. A stopway makes ASDA longer and lets V1 be raised; a clearway makes TODA longer and lets V1 be lowered, and performance software uses these unbalanced fields to find the highest permissible mass (see takeoff speeds V1, VR and V2).

View full schematic

LDA and displaced thresholds

LDA is measured from the landing threshold to the end of the runway available for landing. Neither a stopway nor a clearway is ever part of it.

A displaced threshold is a threshold not located at the beginning of the runway, typically so that approaching airplanes clear obstacles on the approach, or because the pavement before it is unfit for touchdown. It is marked by a white bar across the runway with white arrows on the runway before it, and the edge lights between the runway end and the displaced threshold show red toward the approach. The runway before the bar may be used for taxiing, for the takeoff run and for the landing roll of airplanes coming from the opposite end, but not for touching down.

A displaced threshold therefore shortens the LDA in its own direction and normally leaves the takeoff distances alone. At Chambéry, runway 18 is 2,020 m long and has a TORA of 2,020 m but an LDA of 1,790 m: the threshold is displaced about 230 m. The AIP may also give a second TORA for a takeoff begun at the displaced threshold: Nantes runway 21 has a TORA of 2,853 m from the runway end and 2,591 m from the displaced threshold.

The direction matters. At Nice, the 90 m before the displaced threshold of runway 04L is a runway starter extension: it adds to the TORA of 04L (2,628 m, against an LDA of 2,538 m), but the declared distances of the opposite direction, 22R, end 90 m before the physical end of the runway, so it serves no takeoff or landing on 22R.

Distances can also be cut at the far end. At Chambéry, runway 36 has 1,980 m for takeoff and an LDA of 1,840 m on the same 2,020 m runway, and the AIP gives the reason: reduced declared distances to comply with the runway end safety area requirement. US airports use declared distances in the same way where a full runway safety area cannot be provided. FAA approach charts print the runway landing distance in the briefing strip, the shorter of the declared LDA and the runway length less any displaced threshold: on the ILS to runway 14R at Boeing Field, Seattle, 9,120 ft on a runway 10,007 ft long.

The LDA also sets where the aiming point marking is painted: 150 m beyond the threshold when the LDA is under 800 m, 250 m when it is 800 m to under 1,200 m, 300 m from 1,200 m to under 2,400 m, and 400 m when it is 2,400 m or more.

Intersection takeoffs and reduced distances

An intersection takeoff begins from a taxiway part-way along the runway, so the length behind the intersection is lost from TORA, TODA and ASDA alike, while the LDA is unchanged. Many AIPs publish declared distances for the intersections in common use. From taxiway A3 at Nice, runway 04R offers a TORA and ASDA of 2,473 m and a TODA of 3,013 m: 490 m less than from the full length, with the clearway still counted. The Nice entry states that these distances are measured from the upstream edge of the taxiway where it meets the runway.

Beside the taxiway, a yellow intersection takeoff sign with black characters gives the remaining TORA in meters and an arrow for the direction of takeoff; at French aerodromes under national rules, the sign leaves out the letter m.

None of the declared distances, full-length or intersection, allows for the length an airplane uses up while turning onto the runway. EASA's AMC1 CAT.POL.A.205 asks for a line-up allowance: the position of the main wheels reduces TORA and TODA, and the position of the most forward wheels reduces ASDA. It usually has to be counted after a 90° entry from a taxiway or a 180° turn on the runway.

Declared distances can also be reduced for particular cases:

• Works. A closed section of runway or a temporarily displaced threshold is notified by NOTAM, which gives the distances in force.
• Particular types. At Ajaccio, crews of the Boeing 747, 757 and 767-300 may set takeoff power on runway 20 only after passing a mark, a yellow dashed line with green lights, and must reduce TORA, TODA and ASDA by 92 m.
• Safety areas and obstacles, as at Chambéry.

Performance is calculated with the figures in force on the day, from the AIP and current NOTAM, and a change of runway or intersection during taxi means a new calculation.

Where they are published

In an ICAO-format AIP, each aerodrome entry in Part 3, AD, follows a fixed numbering: AD 2.12 gives the runway physical characteristics, including any clearway and stopway, and AD 2.13 the declared distances for each runway direction, with intersection rows and remarks. Aerodrome and visual approach charts often repeat the table. Some French examples, in meters:

The reading rules are simple: TODA minus TORA is the clearway, ASDA minus TORA is the stopway, and TORA minus LDA is usually a displaced threshold, but the remarks column may give another reason.

In the United States, declared distances are listed in the Chart Supplement. On an FAA airport diagram, a white letter D in a black box means that declared distance information for the runways is in the Chart Supplement.

Comparing available and required distances

Each required distance from the flight manual must fit its declared counterpart, with the factors the operating rules add.

For Performance Class A, EASA's CAT.POL.A.205 and the FAA's 14 CFR 121.189 require all three takeoff checks at once, and whichever binds first sets the field-length-limited mass. The takeoff distance required is the greater of the one-engine-inoperative distance to 35 ft and 115 percent of the all-engines distance. For Performance Class B in commercial operations, CAT.POL.A.305 applies factors instead: a gross takeoff distance of 480 m needs a TORA of at least 600 m when there is no stopway or clearway.

For landing, CAT.POL.A.230 and A.235 require a turbojet to stop within 60 percent of the LDA, so a certified distance of 1,500 m needs an LDA of at least 1,500 ÷ 0.6 = 2,500 m, and about 2,875 m if the runway may be wet; the FAA's 14 CFR 121.195 has the same 60 percent rule. Before the approach, EASA's CAT.OP.MPA.303 adds a check of the landing distance at time of arrival, which the LDA should exceed by at least 15 percent.

On private flights neither EASA's NCO.POL.110 nor the FAA prescribes a factor, but the handbook figures are still compared with TORA and LDA, with a personal margin; 14 CFR 91.103 requires every pilot in command to know the runway lengths at the airports of intended use and the airplane's takeoff and landing distances.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.