LOSS OF RUNWAY LENGTH DUE TO ALIGNMENT
(a) The length of the runway that is declared for the calculation of TODA, ASDA and TORA does not account for line-up of the aeroplane in the direction of take-off on the runway in use. This alignment distance depends on the aeroplane geometry and access possibility to the runway in use. Accountability is usually required for a 90°-taxiway entry to the runway and 180°-turnaround on the runway. There are two distances to be considered:
(1) the minimum distance of the main wheels from the start of the runway for determining TODA and TORA, ‘L’; and
(2) the minimum distance of the most forward wheel(s) from the start of the runway for determining ASDA, ‘N’.
Figure
1
Line-up of the aeroplane in the direction of
take-off — L and N
Where the aeroplane manufacturer does not provide the appropriate data, the calculation method given in (b) may be used to determine the alignment distance.
(b) Alignment distance calculation
The distances mentioned in (a)(1) and (a)(2) above are:
|
|
90°-entry |
180°-turnaround |
|
L = |
RM + X |
RN + Y |
|
N = |
RM + X + WB |
RN + Y + WB |
where:
RN = A + WN = WB/cos(90°-α) + WN
X = safety distance of outer main wheel during turn to the edge of the runway
Y = safety distance of outer nose wheel during turn to the edge of the runway
Note: Minimum edge safety distances for X and Y are specified in FAA AC 150/5300-13 and ICAO Annex 14, 3.8.3
RN = radius of turn of outer nose wheel
RM = radius of turn of outer main wheel
WN = distance from aeroplane centre-line to outer nose wheel
WM = distance from aeroplane centre-line to outer main wheel
WM = wheel base
α = steering angle.