Appendix E to Part 43—Altimeter System Test and Inspection

Each person performing the altimeter system tests and inspections required by §91.411 shall be authorized by 

43.3 and will comply with the following:

(a) Static pressure system and integration:

(1) Ensure freedom from entrapped moisture and restrictions.

(2) Determine that leakage is within the tolerances established in §23.1325 or §25.1325, whichever is

applicable.

(3) Determine that the static port heater, if installed, is operative.

(4) Ensure that no alterations or deformations of the airframe surface have been made that would affect

the relationship between air pressure in the static pressure system and true ambient static air pressure

for any flight condition.

(5) Verify the accuracy of altitude transmissions from the transponder

(b) Altimeter:

(1) Test by an appropriately rated repair facility in accordance with the following subparagraphs. Unless

otherwise specified, each test for performance may be conducted with the instrument subjected to

vibration. When tests are conducted with the temperature substantially different from ambient

temperature of approximately 25 degrees C., allowance shall be made for the variation from the

specified condition.

(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 airplane 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 1 minute, but not more than 10 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 1 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 the corresponding altitude recorded during the scale error test prescribed in paragraph (b)

(i).

(iii) After effect. Not more than 5 minutes after the completion of the hysteresis test prescribed in

paragraph (b)(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 pointers after vibration

shall not exceed the corresponding tolerance listed in Table III.

(v) Case leak. The leakage of the altimeter case, when the pressure within it 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 1 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 the air data computer type with associated computing systems, or which

incorporate air data correction internally, may be tested in a manner and to specifications developed by

the manufacturer which are acceptable to the Administrator.

(c) Automatic Pressure Altitude Reporting Equipment and ATC Transponder System Integration Test.

The test must be conducted by a person rated to perform the checks specified in

paragraph (a). Measure the automatic pressure altitude at the output of the installed ATC transponder

when interrogated on Mode C at a sufficient number of test points to ensure that the altitude reporting

equipment, altimeters, and ATC transponders perform their intended functions as installed in the aircraft.

The difference between the automatic reporting output and the altitude displayed at the altimeter shall
not exceed 125 feet,

or,

Validate the integrity of the digital data bus providing altitude information to the transponder by utilizations of Built 

In test Equipment incorporated within the integrated system framework for the sole purpose of providing diagnostic 

data.

(d) Records: Comply with the provisions of §43.9 of this chapter as to content, form, and disposition of

the 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 persons approving the airplane for

return to service shall enter that data in the airplane log or other permanent record.