1. (a) Unless otherwise prescribed, airplanes must meet the applicable performance requirements of this subpart for ambient atmospheric conditions and still air.

2. (b) The performance, as affected by engine power or thrust, must be based on the following relative humidities;

   1. (1) For turbine engine powered airplanes, a relative humidity of—

      1. (i) 80 percent, at and below standard temperatures; and

      2. (ii) 34 percent, at and above standard temperatures plus 50 °F.

         Between these two temperatures, the relative humidity must vary linearly.

   2. (2) For reciprocating engine powered airplanes, a relative humidity of 80 percent in a standard atmosphere. Engine power corrections for vapor pressure must be made in accordance with the following table:

      Altitude H (ft.)	Vaporpressure e (In. Hg.)	Specific humidity w (Lb. moisture per lb. dry air)	Density ratioρ / σ = 0.0023769
      0	0.403	0.00849	0.99508
      1,000	.354	.00773	.96672
      2,000	.311	.00703	.93895
      3,000	.272	.00638	.91178
      4,000	.238	.00578	.88514
      5,000	.207	.00523	.85910
      6,000	.1805	.00472	.83361
      7,000	.1566	.00425	.80870
      8,000	.1356	.00382	.78434
      9,000	.1172	.00343	.76053
      10,000	.1010	.00307	.73722
      15,000	.0463	.001710	.62868
      20,000	.01978	.000896	.53263
      25,000	.00778	.000436	.44806

3. (c) The performance must correspond to the propulsive thrust available under the particular ambient atmospheric conditions, the particular flight condition, and the relative humidity specified in paragraph (b) of this section. The available propulsive thrust must correspond to engine power or thrust, not exceeding the approved power or thrust less—

   1. (1) Installation losses; and
   2. (2) The power or equivalent thrust absorbed by the accessories and services appropriate to the particular ambient atmospheric conditions and the particular flight condition.
4. (d) Unless otherwise prescribed, the applicant must select the takeoff, en route, approach, and landing configurations for the airplane.
5. (e) The airplane configurations may vary with weight, altitude, and temperature, to the extent they are compatible with the operating procedures required by paragraph (f) of this section.
6. (f) Unless otherwise prescribed, in determining the accelerate-stop distances, takeoff flight paths, takeoff distances, and landing distances, changes in the airplane's configuration, speed, power, and thrust, must be made in accordance with procedures established by the applicant for operation in service.
7. (g) Procedures for the execution of balked landings and missed approaches associated with the conditions prescribed in §§ 25.119 and 25.121(d) must be established.

8. (h) The procedures established under paragraphs (f) and (g) of this section must—

   1. (1) Be able to be consistently executed in service by crews of average skill;
   2. (2) Use methods or devices that are safe and reliable; and
   3. (3) Include allowance for any time delays, in the execution of the procedures, that may reasonably be expected in service.
9. (i) The accelerate-stop and landing distances prescribed in §§ 25.109 and 25.125, respectively, must be determined with all the airplane wheel brake assemblies at the fully worn limit of their allowable wear range.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-38, 41 FR 55466, Dec. 20, 1976; Amdt. 25-92, 63 FR 8318, Feb. 18, 1998]