Part V - Standard 571 Appendix B - Altimeter System Test and Inspection

Canadian Aviation Regulations (CARs) 2017-2

Content last revised: 1996/10/10

The standards of airworthiness applicable to the performance of an altimeter or altimeter system test and inspection are:

(a) For static pressure systems:

(1) the system is free from moisture or sources of restriction;

(2) the static port heater, if installed, is operative;

(3) there is no alteration or deformity of the airframe surface that would affect the relationship between air pressure in the static pressure system and true ambient static air pressure under any flight condition; and

(4) the leakage rate of the system shall not exceed the following tolerances:

(i) for unpressurized aircraft, where the static pressure system is evacuated to a pressure differential of approximately 1 inch of mercury, or to a reading on the altimeter 1000 feet above the aircraft elevation at the time of test, without additional vacuum applied for a period of 1 minute, the loss of indicated altitude must not exceed 100 feet on the altimeter.

(ii) for pressurised aircraft, where the static pressure system is evacuated until a pressure differential equivalent to the maximum cabin pressure differential for which the aircraft is type certified, without additional vacuum applied for a period of 1 minute, the loss of indicated altitude must not exceed 2 percent of the altitude equivalent to the maximum permitted cabin differential pressure, or 100 feet, whichever is greater.

(b) For an altimeter:

(1) Test by an approved maintenance organisation in accordance with the following. Unless otherwise specified, each test for performance may be conducted with the instrument subjected to vibration.

(i) Scale Error

With the barometric pressure scale at 29.92 inches of mercury, the altimeter shall be subjected successively to pressures corresponding to the altitude specified in Table I, up to the maximum normally expected operating altitude of the aircraft in which the altimeter is to be installed. The reduction in pressure shall be made at a rate not in excess of 20,000 feet per minute to within approximately 2,000 feet of the test point. The test point shall be approached at a rate compatible with the test equipment. The altimeter shall be kept at the pressure corresponding to each test point for at least one minute, but not more than ten minutes, before a reading is taken. The error at all test points must not exceed the tolerances specified in Table I.

(ii) Hysteresis

The hysteresis test shall begin not more than 15 minutes after the altimeter's initial exposure to the pressure corresponding to the upper limit of the scale error test prescribed in subparagraph (i); and while the altimeter is at this pressure the hysteresis test shall commence. Pressure shall be increased at a rate simulating a descent in altitude at the rate of 5,000 to 20,000 feet per minute until within 3,000 feet of the first test point (50 percent of maximum altitude). The test point shall then be approached at a rate of approximately 3,000 feet per minute. The altimeter shall be kept at this pressure for at least 5 minutes, but not more than 15 minutes, before the test reading is taken. After the reading has been taken, the pressure shall be increased further, in the same manner as before, until the pressure corresponding to the second test point (40 percent of maximum altitude) is reached. The altimeter shall be kept at this pressure for at least one minute, but not more than 10 minutes, before the test reading is taken. After the reading has been taken, the pressure shall be increased further, in the same manner as before, until atmospheric pressure is reached. The reading of the altimeter at either of the two test points shall not differ by more than the tolerance specified in Table II, from the reading of the altimeter for corresponding altitude recorded during the scale error test prescribed in subparagraph (i).

(iii) After Effect

Not more than 5 minutes after the completion of the hysteresis test prescribed in subparagraph (ii), the reading of the altimeter (corrected for any change in atmospheric pressure) shall not differ from the original atmospheric pressure reading by more than the tolerance specified in Table II.

(iv) Friction

The altimeter shall be subjected to a steady rate of decrease of pressure approximating 750 feet per minute. At each altitude listed in Table III, the change in reading of the points after vibration shall not exceed the corresponding tolerance specified in Table III.

(v) Case Leak

The leakage of the altimeter case, when the pressure within the case corresponds to an altitude of 18,000 feet, shall not change the altimeter reading by more than the tolerance shown in Table II, during an interval of one minute.

(vi) Barometric Scale Error

At constant atmospheric pressure, the barometric pressure scale shall be set at each of the pressures (falling within its range of adjustment) that are listed in Table IV, and shall cause the pointer to indicate the equivalent altitude difference shown in Table IV, with a tolerance of 25 feet.

(2) Altimeters which are of the air data computer type with associated computing systems, or which incorporate internally air data correction, shall be tested and inspected in parts or by major components to specifications developed by the manufacturer.

(c) Records

Comply with Subpart 571 of the CARs as to content, form, and disposition of records. The person performing the altimeter tests shall record on the altimeter the date and maximum altitude to which the altimeter has been tested and the person signing the maintenance release shall enter that data in the aircraft record.

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