When you have the V-Speeds, how do you then know if the runway is acceptable for your specific case?

Question

When you have the V-Speeds, how do you then know if the runway is acceptable for your specific case?

Answer 1

The V-speeds are actually determined by the runway itself.

For instance, if you are operating off of a short field, you must adjust V1 to ensure that if an engine failure were to occur at it, a stop could be made on the remaining runway and clearway.

For every single flight, this data must be calculated for each possible runway of use.  If takeoff data is not available for a given runway, we may not operate off of it and must use another one.  You will often hear pilots talking about "having the numbers" for a runway or "waiting for the numbers" if they have an ACARS system installed.  That is what they are doing.  They are making sure they have performance numbers for a particular runway.  If they do not have them, or if they cannot meet the restrictions imposed on them to use a particular runway (eg...airplane is too heavy to use a runway) then they must use another one or get the numbers another way.  Sometimes they can call dispatch on the phone or sent messages via an ACARS.

Answer 2

The short answer is that you calculate the runway length required from the takeoff performance charts found in the Pilots Operating Handbook (POH) and compare it to the runway length available. The main reference chart many aircraft use is  called Accelerate-Stop Distance which is the total distance required to bring the airplane to a stop if you abort the takeoff just prior to reaching V1 (takeoff decision speed). In the USA, a Part 135 or 121 air carrier is required to add 15% to the calculated distance for an extra margin of safety.

Answer 3

Pilots Operating Handbook. AKA POH

Answer 4

The V-Speeds are all computed using the Aircraft Flight Manual (AFM).  While computing the V-speeds, pilots also compute the takeoff distance required.  What the distance is depends on how the manufacturer presents the data.

Some planes use a TOFL (TakeOff Field Length).  This is the longest distance of:

-Normal takeoff distance to 35 ft height + 15%

-Distance to accelerate to V1 and then come to a complete stop

-Takeoff distance to 35 ft height following an engine failure at V1

Other planes use "Balanced Field Length".  A balanced field length achieved when V1 is selected so that the accelerate-stop distance is equal to the accelerate-go distance.

When using either of these methods, the runway available must be greater than the calculated TOFL/Balanced Field Length.

There are ways of using an unbalanced field length, but that goes beyond the scope of a simple answer.

Calculating V-speeds and TOFL/Balanced Field Length does take into account aircraft weight, takeoff flap setting, runway slope, runway condition (i.e. contamination), pressure altitude, temperature, wind, if all aircraft equipment is operational and/or operating (i.e. anti-skid, engine anti-ice), and so on.

After all of that background, here's the answer to your question.  We compute how much runway we need using one of the methods above.  If the runway length is limiting, we figure out what our maximum takeoff weight is for the given conditions and fuel the aircraft accordingly.  This may mean making an extra fuel stop so we can make the takeoff at a lighter weight if we are runway limited.  And yes, it is possible to have days where the trip just might not work (i.e. 95 degrees in Aspen).