Certification Checks

This paragraph sets when the whole rule applies: an airplane or helicopter operated in controlled airspace under IFR. An airplane flown only under VFR does not need this test. Paragraphs (1), (2) and (3) are the three things that must be true before that flight.

This is the 24-month test. Each static pressure system, each altimeter and each automatic pressure altitude reporting system (the altitude encoder) must have been tested and inspected within the preceding 24 calendar months. The paragraph names Appendices E and F of Part 43; the altimeter system test itself is laid out in Appendix E.

Any time the static system is opened and closed, for example to replace an instrument or a fitting, the static system is tested and inspected again to Appendix E, paragraph (a), before the next IFR flight in controlled airspace. Using the system drain and the alternate static pressure valve are the two exceptions.

After an encoder is installed or worked on in a way that could cause a data correspondence error, the encoder, the altimeters and the transponder are tested together to Appendix E, paragraph (c), the correspondence test. A data correspondence error is a difference between the altitude the transponder sends and the altitude the altimeter shows.

This paragraph begins the list of who may conduct the tests in paragraph (a). Only the persons in (1), (2) and (3) may do them.

The company that built the airplane or helicopter may test it.

A repair station certificated under 14 CFR Part 145 may do the tests if it has the equipment the work needs (properly equipped) and holds one of the four ratings listed under this paragraph.

An instrument rating, Class I, covers mechanical instruments such as altimeters and airspeed indicators. 14 CFR 145.59(e)(1) writes the same rating as Class 1.

A limited instrument rating covers only the makes and models of instruments the repair station is rated for. The appliance here is the instrument being tested, such as the altimeter or the encoder.

A limited rating for the test itself lets a repair station perform this test without holding the full instrument rating.

A repair station with an airframe rating for the airplane or helicopter being tested may do the whole 91.411 test. This is a repair station rating, not a mechanic’s rating.

A mechanic with an airframe rating may do the static pressure system tests and inspections, Appendix E, paragraph (a), and nothing more. The altimeter test and the correspondence test go to the persons in (1) and (2).

An altimeter or encoder approved under a Technical Standard Order (TSO), the FAA’s minimum performance standard for a part, counts as tested and inspected on the date it was made. Installing it still opens the static system, so the static system test in (a)(2) still follows, and a new encoder also needs the correspondence test in (a)(3).

Under IFR in controlled airspace, the airplane may not fly above the highest altitude to which all of its altimeters and its encoder were tested. That altitude is marked on the altimeter and entered in the record (Appendix E, paragraph (d)).

Appendix E is the test standard for 91.411. Everyone who performs the altimeter system tests and inspections follows it.

Paragraph (a) is the static system part of the test. It is the part a mechanic with an airframe rating may do (91.411(b)(3)), and the test that follows any opening of the static system (91.411(a)(2)).

Check the static lines for trapped water and for anything that blocks them.

Prove that the static system holds pressure, by a method the FAA accepts. The airplane maker’s instructions come first. When there are none, AC 43.13-1B, paragraph 12-58, gives a method: apply a vacuum equal to 1,000 feet of altitude and hold it; after 1 minute the leak must not exceed the equal of 100 feet. For transport category airplanes, certificated under Part 25, the leak limit is in 14 CFR 25.1325.

If the static ports are heated, check that the heater works.

Check that no dent, repair or change to the skin near the static ports could change the pressure the ports sense.

Paragraph (b) is the altimeter part of the test.

The altimeter is tested by a repair facility with the right rating, through tests (i) to (vi). The instrument may be vibrated during the tests, which keeps friction from holding the pointer. If the room is far from about 25 degrees Celsius (77 degrees Fahrenheit), the readings are corrected for it.

Scale error is the main altimeter test. With the barometric scale set to 29.92 inches of mercury, the test set takes the altimeter to each altitude in Table I, up to the highest altitude the airplane is normally expected to fly. At each test point the reading must be within the Table I tolerance. The highest altitude reached is the maximum altitude tested.

Hysteresis is a lag in the reading on the way back down. After the top test point, the test set brings the altimeter down to 50 percent and then 40 percent of the maximum altitude, and each reading must agree with the scale error reading at that altitude within 75 feet (Table II).

After effect: within 5 minutes of the hysteresis test, back at the starting pressure, the altimeter must return to its first reading within 30 feet (Table II).

Friction: as the pressure falls at about 750 feet per minute, vibrating the instrument must not move the pointers more than the Table III tolerance.

Case leak: with the inside of the case at the pressure of 18,000 feet, a leak in the altimeter case must not change the reading more than 100 feet in 1 minute (Table II).

Barometric scale error: the scale the pilot sets to the local pressure is set to each pressure in Table IV, and the pointer must move by the altitude difference listed, within 25 feet.

An altimeter that is part of an air data computer system, or that corrects its own reading, may be tested by the manufacturer’s method and limits, when the FAA accepts them. Many glass cockpits use air data computers, and this paragraph covers them.

Paragraph (c) is the correspondence test, done by an appropriately rated person under the conditions of paragraph (a). The altitude at the transponder’s output, read on Mode C, is compared with the altimeter at enough test points to show that the encoder, the altimeters and the transponder work as installed. The two may differ by no more than 125 feet.

The record rule. The entry follows 43.9. The person who tests the altimeter marks the test date and the maximum altitude tested on the altimeter, and the person who approves the airplane for return to service enters the same date and altitude in the airplane’s record.

This is an operating rule for the altitude encoder wired to the transponder. Each item under it names a case in which the encoder may not be operated.

When air traffic control tells the pilot to turn the altitude reporting off, it stays off.

The encoder, as installed, must have been tested and calibrated to send altitude within 125 feet of the altimeter the pilot flies by, with that altimeter set to 29.92 inches of mercury, from sea level to the aircraft’s maximum operating altitude. On a 95 percent probability basis means at least 95 of every 100 readings agree within 125 feet. The correspondence test in Appendix E, paragraph (c), checks the same 125 feet.

This paragraph names the Technical Standard Orders for the parts: TSO-C10b for altimeters and TSO-C88 for digitizers, the part of the encoder that turns pressure altitude into a code.

When an aircraft has both a transponder and ADS-B Out, the pressure altitude both of them report must come from the same source. ADS-B Out (Automatic Dependent Surveillance-Broadcast Out) is equipment that broadcasts the aircraft’s position and altitude to air traffic control and to other aircraft.

The transponder may not be used unless it was tested and inspected to Appendix F within the preceding 24 calendar months. The rule says use, not IFR, so it applies on any flight with the transponder on, VFR or IFR. Sections 91.215(a), 121.345(c) and 135.143(c) set the equipment standards for installed transponders, so this covers the transponder installed in the aircraft.

After a transponder is installed or worked on in a way that could cause a data correspondence error, the transponder, the encoder and the altimeters are tested together to Appendix E, paragraph (c), the correspondence test.

This paragraph begins the list of who may conduct the transponder tests. A mechanic is not on the list.

A repair station certificated under 14 CFR Part 145 may do the tests if it has the equipment the work needs and holds one of the three ratings listed under this paragraph.

A radio rating, Class III, covers radar equipment, the systems that work on pulsed radio signals, such as the transponder. 14 CFR 145.59(d)(3) writes the same rating as Class 3.

A limited radio rating covers only the makes and models of transponder the repair station is rated for.

A limited rating for the test itself lets a repair station perform the transponder test without holding the full radio rating.

An operator that maintains its aircraft under a continuous airworthiness maintenance program may test its own transponders. Airlines under Part 121 have that program, and so do charter operators under 135.411(a)(2), which covers aircraft with ten or more passenger seats.

The aircraft manufacturer may test the transponder only if the manufacturer installed it.

The 91.413 test may be done in the shop with the transponder removed from the aircraft, or in the aircraft with a portable test set coupled to the transponder antenna. With a portable test set, the interrogation rate is kept low (235 per second for Mode A and Mode C, 50 per second for Mode S) so the test does not disturb real radar, and 3 decibels more loss is allowed in the sensitivity test for the antenna coupling. ATCRBS (Air Traffic Control Radar Beacon System) is the Mode A and Mode C system, so an ATCRBS transponder is a Mode A or Mode C transponder.

The reply frequency test.

A Mode A or Mode C transponder must reply on 1090 megahertz (MHz), plus or minus 3 MHz.

Class 1B, 2B and 3B Mode S transponders must also reply within 3 MHz of 1090 MHz. A Mode S (Mode Select) transponder also replies to interrogations addressed to its own aircraft.

A Class 1B, 2B or 3B Mode S transponder built with the optional 1 MHz reply frequency must meet that tighter limit.

Class 1A, 2A, 3A and 4 Mode S transponders must reply within 1 MHz of 1090 MHz.

The suppression test. The ground radar sends its interrogation pulses, P1 and P3, in its narrow main beam, and a suppression pulse, P2, from an antenna that sends in all directions. A transponder off to the side of the main beam receives P2 as strong as P1 and must not reply. The rates in this paragraph set how fast the test set interrogates.

With P2 as strong as P1, the transponder may reply to no more than 1 percent of the interrogations.

With P2 9 decibels (dB) weaker than P1, the transponder must reply to at least 90 percent. A decibel compares two signal strengths; 9 dB weaker is about one eighth of the power.

The receiver sensitivity test.

The minimum triggering level (MTL) is the weakest interrogation the transponder replies to. It must be minus 73 dBm, plus or minus 4, for a Mode A or Mode C transponder, and minus 74 dBm, plus or minus 3, for Mode S. dBm is radio power in decibels compared with 1 milliwatt.

Method one: the test set connects where the transmission line, the antenna cable, meets the antenna.

Method two: the test set connects at the transponder’s antenna connector, and the loss in the cable is added in.

Method three: the test set sends its signal through the air to the aircraft antenna.

Sensitivity on Mode 3/A (the identity code mode) and on Mode C (the altitude mode) may differ by no more than 1 decibel.

The peak power test, the strength of the reply.

The reply power must be inside the limits for the class of transponder, measured by one of the three methods in (c)(1).

Class 1A and 2A Mode A or Mode C transponders: at least 125 watts (21.0 dBW). dBW is power in decibels compared with 1 watt.

Class 1B and 2B Mode A or Mode C transponders: at least 70 watts (18.5 dBW).

Class 1A, 2A, 3A and 4 Mode S transponders, and Class 1B, 2B and 3B Mode S transponders with the optional high power: at least 125 watts.

Class 1B, 2B and 3B Mode S transponders: at least 70 watts.

No transponder of any class may send more than 500 watts (27.0 dBW).

Diversity means two antennas, one on top of the aircraft and one on the bottom. The selected antenna must send at least 20 dB more power than the one not selected.

Every Mode S transponder has its own address, a code assigned to one aircraft. It must reply to its own address and ignore at least two wrong ones.

Mode S interrogations come in numbered uplink formats (UF). In replies to format 4 the altitude must match the Mode C reply, and in replies to format 5 the identity code must match the Mode A reply.

In an all-call, the ground asks every Mode S transponder to answer. The reply (downlink format 11) must carry the right address and capability.

A Mode S transponder must not answer the all-call meant only for Mode A and Mode C transponders, the one with a short 0.8 microsecond P4 pulse.

A squitter is a short signal the Mode S transponder sends on its own, without being asked, about once a second, so ground stations and other aircraft can find it.

The record rule for the transponder test: follow 43.9. There is no altitude to mark, as there is for the altimeter.

This paragraph sets when the whole rule applies: an airplane or helicopter operated in controlled airspace under IFR. An airplane flown only under VFR does not need this test. Paragraphs (1), (2) and (3) are the three things that must be true before that flight.

This is the 24-month test. Each static pressure system, each altimeter and each automatic pressure altitude reporting system (the altitude encoder) must have been tested and inspected within the preceding 24 calendar months. The paragraph names Appendices E and F of Part 43; the altimeter system test itself is laid out in Appendix E.

Any time the static system is opened and closed, for example to replace an instrument or a fitting, the static system is tested and inspected again to Appendix E, paragraph (a), before the next IFR flight in controlled airspace. Using the system drain and the alternate static pressure valve are the two exceptions.

After an encoder is installed or worked on in a way that could cause a data correspondence error, the encoder, the altimeters and the transponder are tested together to Appendix E, paragraph (c), the correspondence test. A data correspondence error is a difference between the altitude the transponder sends and the altitude the altimeter shows.

This paragraph begins the list of who may conduct the tests in paragraph (a). Only the persons in (1), (2) and (3) may do them.

The company that built the airplane or helicopter may test it.

A repair station certificated under 14 CFR Part 145 may do the tests if it has the equipment the work needs (properly equipped) and holds one of the four ratings listed under this paragraph.

An instrument rating, Class I, covers mechanical instruments such as altimeters and airspeed indicators. 14 CFR 145.59(e)(1) writes the same rating as Class 1.

A limited instrument rating covers only the makes and models of instruments the repair station is rated for. The appliance here is the instrument being tested, such as the altimeter or the encoder.

A limited rating for the test itself lets a repair station perform this test without holding the full instrument rating.

A repair station with an airframe rating for the airplane or helicopter being tested may do the whole 91.411 test. This is a repair station rating, not a mechanic’s rating.

A mechanic with an airframe rating may do the static pressure system tests and inspections, Appendix E, paragraph (a), and nothing more. The altimeter test and the correspondence test go to the persons in (1) and (2).

An altimeter or encoder approved under a Technical Standard Order (TSO), the FAA’s minimum performance standard for a part, counts as tested and inspected on the date it was made. Installing it still opens the static system, so the static system test in (a)(2) still follows, and a new encoder also needs the correspondence test in (a)(3).

Under IFR in controlled airspace, the airplane may not fly above the highest altitude to which all of its altimeters and its encoder were tested. That altitude is marked on the altimeter and entered in the record (Appendix E, paragraph (d)).

The transponder may not be used unless it was tested and inspected to Appendix F within the preceding 24 calendar months. The rule says use, not IFR, so it applies on any flight with the transponder on, VFR or IFR. Sections 91.215(a), 121.345(c) and 135.143(c) set the equipment standards for installed transponders, so this covers the transponder installed in the aircraft.

After a transponder is installed or worked on in a way that could cause a data correspondence error, the transponder, the encoder and the altimeters are tested together to Appendix E, paragraph (c), the correspondence test.

This paragraph begins the list of who may conduct the transponder tests. A mechanic is not on the list.

A repair station certificated under 14 CFR Part 145 may do the tests if it has the equipment the work needs and holds one of the three ratings listed under this paragraph.

A radio rating, Class III, covers radar equipment, the systems that work on pulsed radio signals, such as the transponder. 14 CFR 145.59(d)(3) writes the same rating as Class 3.

A limited radio rating covers only the makes and models of transponder the repair station is rated for.

A limited rating for the test itself lets a repair station perform the transponder test without holding the full radio rating.

An operator that maintains its aircraft under a continuous airworthiness maintenance program may test its own transponders. Airlines under Part 121 have that program, and so do charter operators under 135.411(a)(2), which covers aircraft with ten or more passenger seats.

The aircraft manufacturer may test the transponder only if the manufacturer installed it.

Each person who maintains, does preventive maintenance on, rebuilds or alters an aircraft or a part makes an entry in its maintenance record with the four items below. Appendix E, paragraph (d), and Appendix F, paragraph (k), send the 91.411 and 91.413 tests to this section for their records.

What was done, or a reference to data the FAA accepts that describes it. For these tests, the entry names the test and the rule and appendix it was done to.

The date the work was finished. The 24 calendar months are counted from this month.

The name of the person who did the work, when that person is not the one who signs.

When the work is satisfactory: the signature, certificate number and kind of certificate of the person approving it. The signature is the approval for return to service for the work in this entry only.

Airlines and charter operators with a continuous airworthiness maintenance program keep their maintenance records under their own Part 121 or Part 135 rules.

Inspections under Part 91, such as the annual and the 100-hour inspection, are recorded under 43.11, not this section. The 91.411 and 91.413 tests still use this section, because Appendix E, paragraph (d), and Appendix F, paragraph (k), say so.

A major repair or a major alteration is also written up on a form, FAA Form 337, as Appendix B of Part 43 describes.

Appendix E is the test standard for 91.411. Everyone who performs the altimeter system tests and inspections follows it.

Paragraph (a) is the static system part of the test. It is the part a mechanic with an airframe rating may do (91.411(b)(3)), and the test that follows any opening of the static system (91.411(a)(2)).

Check the static lines for trapped water and for anything that blocks them.

Prove that the static system holds pressure, by a method the FAA accepts. The airplane maker’s instructions come first. When there are none, AC 43.13-1B, paragraph 12-58, gives a method: apply a vacuum equal to 1,000 feet of altitude and hold it; after 1 minute the leak must not exceed the equal of 100 feet. For transport category airplanes, certificated under Part 25, the leak limit is in 14 CFR 25.1325.

If the static ports are heated, check that the heater works.

Check that no dent, repair or change to the skin near the static ports could change the pressure the ports sense.

Paragraph (b) is the altimeter part of the test.

The altimeter is tested by a repair facility with the right rating, through tests (i) to (vi). The instrument may be vibrated during the tests, which keeps friction from holding the pointer. If the room is far from about 25 degrees Celsius (77 degrees Fahrenheit), the readings are corrected for it.

Scale error is the main altimeter test. With the barometric scale set to 29.92 inches of mercury, the test set takes the altimeter to each altitude in Table I, up to the highest altitude the airplane is normally expected to fly. At each test point the reading must be within the Table I tolerance. The highest altitude reached is the maximum altitude tested.

Hysteresis is a lag in the reading on the way back down. After the top test point, the test set brings the altimeter down to 50 percent and then 40 percent of the maximum altitude, and each reading must agree with the scale error reading at that altitude within 75 feet (Table II).

After effect: within 5 minutes of the hysteresis test, back at the starting pressure, the altimeter must return to its first reading within 30 feet (Table II).

Friction: as the pressure falls at about 750 feet per minute, vibrating the instrument must not move the pointers more than the Table III tolerance.

Case leak: with the inside of the case at the pressure of 18,000 feet, a leak in the altimeter case must not change the reading more than 100 feet in 1 minute (Table II).

Barometric scale error: the scale the pilot sets to the local pressure is set to each pressure in Table IV, and the pointer must move by the altitude difference listed, within 25 feet.

An altimeter that is part of an air data computer system, or that corrects its own reading, may be tested by the manufacturer’s method and limits, when the FAA accepts them. Many glass cockpits use air data computers, and this paragraph covers them.

Paragraph (c) is the correspondence test, done by an appropriately rated person under the conditions of paragraph (a). The altitude at the transponder’s output, read on Mode C, is compared with the altimeter at enough test points to show that the encoder, the altimeters and the transponder work as installed. The two may differ by no more than 125 feet.

The record rule. The entry follows 43.9. The person who tests the altimeter marks the test date and the maximum altitude tested on the altimeter, and the person who approves the airplane for return to service enters the same date and altitude in the airplane’s record.

The 91.413 test may be done in the shop with the transponder removed from the aircraft, or in the aircraft with a portable test set coupled to the transponder antenna. With a portable test set, the interrogation rate is kept low (235 per second for Mode A and Mode C, 50 per second for Mode S) so the test does not disturb real radar, and 3 decibels more loss is allowed in the sensitivity test for the antenna coupling. ATCRBS (Air Traffic Control Radar Beacon System) is the Mode A and Mode C system, so an ATCRBS transponder is a Mode A or Mode C transponder.

The reply frequency test.

A Mode A or Mode C transponder must reply on 1090 megahertz (MHz), plus or minus 3 MHz.

Class 1B, 2B and 3B Mode S transponders must also reply within 3 MHz of 1090 MHz. A Mode S (Mode Select) transponder also replies to interrogations addressed to its own aircraft.

A Class 1B, 2B or 3B Mode S transponder built with the optional 1 MHz reply frequency must meet that tighter limit.

Class 1A, 2A, 3A and 4 Mode S transponders must reply within 1 MHz of 1090 MHz.

The suppression test. The ground radar sends its interrogation pulses, P1 and P3, in its narrow main beam, and a suppression pulse, P2, from an antenna that sends in all directions. A transponder off to the side of the main beam receives P2 as strong as P1 and must not reply. The rates in this paragraph set how fast the test set interrogates.

With P2 as strong as P1, the transponder may reply to no more than 1 percent of the interrogations.

With P2 9 decibels (dB) weaker than P1, the transponder must reply to at least 90 percent. A decibel compares two signal strengths; 9 dB weaker is about one eighth of the power.

The receiver sensitivity test.

The minimum triggering level (MTL) is the weakest interrogation the transponder replies to. It must be minus 73 dBm, plus or minus 4, for a Mode A or Mode C transponder, and minus 74 dBm, plus or minus 3, for Mode S. dBm is radio power in decibels compared with 1 milliwatt.

Method one: the test set connects where the transmission line, the antenna cable, meets the antenna.

Method two: the test set connects at the transponder’s antenna connector, and the loss in the cable is added in.

Method three: the test set sends its signal through the air to the aircraft antenna.

Sensitivity on Mode 3/A (the identity code mode) and on Mode C (the altitude mode) may differ by no more than 1 decibel.

The peak power test, the strength of the reply.

The reply power must be inside the limits for the class of transponder, measured by one of the three methods in (c)(1).

Class 1A and 2A Mode A or Mode C transponders: at least 125 watts (21.0 dBW). dBW is power in decibels compared with 1 watt.

Class 1B and 2B Mode A or Mode C transponders: at least 70 watts (18.5 dBW).

Class 1A, 2A, 3A and 4 Mode S transponders, and Class 1B, 2B and 3B Mode S transponders with the optional high power: at least 125 watts.

Class 1B, 2B and 3B Mode S transponders: at least 70 watts.

No transponder of any class may send more than 500 watts (27.0 dBW).

Diversity means two antennas, one on top of the aircraft and one on the bottom. The selected antenna must send at least 20 dB more power than the one not selected.

Every Mode S transponder has its own address, a code assigned to one aircraft. It must reply to its own address and ignore at least two wrong ones.

Mode S interrogations come in numbered uplink formats (UF). In replies to format 4 the altitude must match the Mode C reply, and in replies to format 5 the identity code must match the Mode A reply.

In an all-call, the ground asks every Mode S transponder to answer. The reply (downlink format 11) must carry the right address and capability.

A Mode S transponder must not answer the all-call meant only for Mode A and Mode C transponders, the one with a short 0.8 microsecond P4 pulse.

A squitter is a short signal the Mode S transponder sends on its own, without being asked, about once a second, so ground stations and other aircraft can find it.

The record rule for the transponder test: follow 43.9. There is no altitude to mark, as there is for the altimeter.