---
kind: "range"
citation: "14 C.F.R. §§ 27.1041–27.1045"
title: "14"
from: "27.1041"
to: "27.1045"
count: 3
url: "https://uscodex.org/cfr/14/27.1041..27.1045"
---

# §27.1041. General.

- (a) Each powerplant cooling system must be able to maintain the temperatures of powerplant components within the limits established for these components under critical surface (ground or water) and flight operating conditions for which certification is required and after normal shutdown. Powerplant components to be considered include but may not be limited to engines, rotor drive system components, auxiliary power units, and the cooling or lubricating fluids used with these components.
- (b) Compliance with [paragraph (a)](#a) of this section must be shown in tests conducted under the conditions prescribed in that paragraph.

# §27.1043. Cooling tests.

- (a) **General.** For the tests prescribed in [§ 27.1041(b)](/cfr/14/27.1041.md?p=b), the following apply:
  - (1) If the tests are conducted under conditions deviating from the maximum ambient atmospheric temperature specified in [paragraph (b)](#b) of this section, the recorded powerplant temperatures must be corrected under paragraphs [(c)](#c) and [(d)](#d) of this section unless a more rational correction method is applicable.
  - (2) No corrected temperature determined under [paragraph (a)(1)](#a-1) of this section may exceed established limits.
  - (3) For reciprocating engines, the fuel used during the cooling tests must be of the minimum grade approved for the engines, and the mixture settings must be those normally used in the flight stages for which the cooling tests are conducted.
  - (4) The test procedures must be as prescribed in [§ 27.1045](/cfr/14/27.1045.md).
- (b) **Maximum ambient atmospheric temperature.** A maximum ambient atmospheric temperature corresponding to sea level conditions of at least 100 degrees F. must be established. The assumed temperature lapse rate is 3.6 degrees F. per thousand feet of altitude above sea level until a temperature of −69.7 degrees F. is reached, above which altitude the temperature is considered constant at −69.7 degrees F. However, for winterization installations, the applicant may select a maximum ambient atmospheric temperature corresponding to sea level conditions of less than 100 degrees F.
- (c) **Correction factor (except cylinder barrels).** Unless a more rational correction applies, temperatures of engine fluids and power-plant components (except cylinder barrels) for which temperature limits are established, must be corrected by adding to them the difference between the maximum ambient atmospheric temperature and the temperature of the ambient air at the time of the first occurrence of the maximum component or fluid temperature recorded during the cooling test.
- (d) **Correction factor for cylinder barrel temperatures.** Cylinder barrel temperatures must be corrected by adding to them 0.7 times the difference between the maximum ambient atmospheric temperature and the temperature of the ambient air at the time of the first occurrence of the maximum cylinder barrel temperature recorded during the cooling test.

# §27.1045. Cooling test procedures.

- (a) **General.** For each stage of flight, the cooling tests must be conducted with the rotorcraft—
  - (1) In the configuration most critical for cooling; and
  - (2) **Under the conditions most critical for cooling.**
- (b) **Temperature stabilization.** For the purpose of the cooling tests, a temperature is “stabilized” when its rate of change is less than two degrees F. per minute. The following component and engine fluid temperature stabilization rules apply:
  - (1) **For each rotorcraft, and for each stage of flight—**
    - (i) The temperatures must be stabilized under the conditions from which entry is made into the stage of flight being investigated; or
    - (ii) If the entry condition normally does not allow temperatures to stabilize, operation through the full entry condition must be conducted before entry into the stage of flight being investigated in order to allow the temperatures to attain their natural levels at the time of entry.
  - (2) For each helicopter during the takeoff stage of flight, the climb at takeoff power must be preceded by a period of hover during which the temperatures are stabilized.
- (c) **Duration of test.** For each stage of flight the tests must be continued until—
  - (1) The temperatures stabilize or 5 minutes after the occurrence of the highest temperature recorded, as appropriate to the test condition;
  - (2) That stage of flight is completed; or
  - (3) **An operating limitation is reached.**