CS 25.109 Accelerate-stop distance

ED Decision 2016/010/R

(See AMC 25.109)

(a)     (See AMC 25.109(a) and (b).) The accelerate-stop distance on a dry runway is the greater of the following distances:

(1)     The sum of the distances necessary to –

(i)      Accelerate the aeroplane from a standing start with all engines operating to V_EF for take-off from a dry runway;

(ii)     Allow the aeroplane to accelerate from V_EF to the highest speed reached during the rejected take-off, assuming the critical engine fails at V_EF and the pilot takes the first action to reject the take-off at the V₁ for take-off from a dry runway; and

(iii)     Come to a full stop on a dry runway from the speed reached as prescribed in sub-paragraph (a)(1)(ii) of this paragraph; plus

(iv)     A distance equivalent to 2 seconds at the V₁ for take-off from a dry runway.

(2)     The sum of the distances necessary to –

(i)      Accelerate the aeroplane from a standing start with all engines operating to the highest speed reached during the rejected take-off, assuming the pilot takes the first action to reject the take-off at the V₁ for take-off from a dry runway; and

(ii)     With all engines still operating, come to a full stop on a dry runway from the speed reached as prescribed in sub-paragraph (a)(2)(i) of this paragraph; plus

(iii)     A distance equivalent to 2 seconds at the V₁ for take-off from a dry runway.

(b)     (See AMC 25.109(a) and (b).) The accelerate-stop distance on a wet runway is the greater of the following distances:

(1)     The accelerate-stop distance on a dry runway determined in accordance with sub-paragraph (a) of this paragraph; or

(2)     The accelerate-stop distance determined in accordance with sub-paragraph (a) of this paragraph, except that the runway is wet and the corresponding wet runway values of V_EF and V₁ are used. In determining the wet runway accelerate-stop distance, the stopping force from the wheel brakes may never exceed:

(i)      The wheel brakes stopping force determined in meeting the requirements of CS 25.101(i) and sub-paragraph (a) of this paragraph; and

(ii)     The force resulting from the wet runway braking coefficient of friction determined in accordance with subparagraphs (c) or (d) of this paragraph, as applicable, taking into account the distribution of the normal load between braked and unbraked wheels at the most adverse centre of gravity position approved for take-off.

(c)      The wet runway braking coefficient of friction for a smooth wet runway is defined as a curve of friction coefficient versus ground speed and must be computed as follows:

(1)     The maximum tyre-to-ground wet runway braking coefficient of friction is defined as (see Figure 1):

Figure 1

where:

Tyre Pressure = maximum aeroplane operating tyre pressure (psi)

µ_t/gMAX = maximum tyre-to-ground braking coefficient

V = aeroplane true ground speed (knots); and

Linear interpolation may be used for tyre pressures other than those listed.

(2)     (See AMC 25.109(c)(2) The maximum tyre-to-ground wet runway braking coefficient of friction must be adjusted to take into account the efficiency of the anti-skid system on a wet runway. Anti-skid system operation must be demonstrated by flight testing on a smooth wet runway and its efficiency must be determined. Unless a specific anti-skid system efficiency is determined from a quantitative analysis of the flight testing on a smooth wet runway, the maximum tyre-to-ground wet runway braking coefficient of friction determined in sub-paragraph (c)(1) of this paragraph must be multiplied by the efficiency value associated with the type of anti-skid system installed on the aeroplane:

(d)     At the option of the applicant, a higher wet runway braking coefficient of friction may be used for runway surfaces that have been grooved or treated with a porous friction course material. For grooved and porous friction course runways,

(1)     70% of the dry runway braking coefficient of friction used to determine the dry runway accelerate-stop distance; or

(2)     (See AMC 25.109(d)(2).) The wet runway braking coefficient of friction defined in sub-paragraph (c) of this paragraph, except that a specific anti-skid efficiency, if determined, is appropriate for a grooved or porous friction course wet runway and the maximum tyre-to-ground wet runway braking coefficient of friction is defined as (see Figure 2):

Figure 2

where:

Tyre Pressure = maximum aeroplane operating tyre pressure (psi)

µ_t/gMAX = maximum tyre-to-ground braking coefficient

V   =   aeroplane true ground speed (knots); and Linear interpolation may be used for tyre pressures other than those listed.

(e)     Except as provided in sub-paragraph (f)(1) of this paragraph, means other than wheel brakes may be used to determine the accelerate-stop distance if that means –

(1)     Is safe and reliable;

(2)     Is used so that consistent results can be expected under normal operating conditions; and

(3)     Is such that exceptional skill is not required to control the aeroplane.

(f)      The effects of available reverse thrust –

(1)     Must not be included as an additional means of deceleration when determining the accelerate-stop distance on a dry runway; and

(2)     May be included as an additional means of deceleration using recommended reverse thrust procedures when determining the accelerate-stop distance on a wet runway, provided the requirements of sub-paragraph (e) of this paragraph are met. (See AMC 25.109(f).)

(g)     The landing gear must remain extended throughout the accelerate-stop distance.

(h)     If the accelerate-stop distance includes a stopway with surface characteristics substantially different from those of the runway, the take-off data must include operational correction factors for the accelerate-stop distance. The correction factors must account for the particular surface characteristics of the stopway and the variations in these characteristics with seasonal weather conditions (such as temperature, rain, snow and ice) within the established operational limits.

(i)      A flight test demonstration of the maximum brake kinetic energy accelerate-stop distance must be conducted with not more than 10% of the allowable brake wear range remaining on each of the aeroplane wheel brakes.

[Amdt 25/18]