Communications, Light Signals, and Runway Lighting Systems — FAA A&P Test Questions (ACS AM.II.I)

This Airframe subject area bundles three things a mechanic has to know cold: communication and navigation radio installations, the light gun signals a tower uses when radios fail, and the colors of runway and taxiway lighting. The test questions are mostly straight recall. What does a flashing red light mean to an aircraft on the ground, what frequency does a modern emergency locator transmitter use, what color are taxiway edge lights, and why must an antenna base be bonded to structure. Learn the colors and frequencies as a table and this area goes quickly.

What ACS AM.II.I covers

AM.II.I draws on the communication, navigation, and airport lighting material in FAA-H-8083-31. Radio installation is one block: antenna location and orientation, coaxial cable and connector care, and bonding. Bonding an antenna base to structure matters because the skin acts as the ground plane and the return path for radio frequency current; poor bonding degrades the radiation pattern, raises standing wave ratio, and lets precipitation static and electrical noise into the receiver. You should also know the frequency bands. VHF communication runs from 118 to about 137 megahertz, and VHF navigation occupies roughly 108 to 118 megahertz, so a frequency such as 112.1 megahertz belongs to a VOR. Emergency locator transmitters are a second block. A modern ELT alerts search and rescue with a coded digital signal on 406 megahertz and also transmits on 121.5 megahertz as a homing signal. Questions cover the purpose of the unit, activation by an impact-sensing switch, inspection intervals, and battery replacement. Light gun signals are third. A steady green clears an aircraft for takeoff on the ground and clears it to land in flight, flashing green means cleared to taxi on the ground, steady red means stop on the ground, and flashing red on the ground means taxi clear of the runway in use. Flashing white applies only on the ground and means return to the starting point on the airport. Airport lighting closes the area. Runway edge lights are white, with the final section of an instrument runway shown amber as a caution zone. Threshold lights show green to an aircraft approaching to land and red as runway end lights from the other side. Taxiway edge lights are blue, and taxiway centerline lights are green.

Where this sits on the test

ACS AM.II.I is tested on the FAA Airframe written test, one of 1,748 ACS-tagged questions in the Airframe bank. Every question tagged to this area carries a worked rationale and its FAA handbook reference, so you can drill the code itself rather than the whole test.

FAA handbook references

  • FAA-H-8083-31

Three traps candidates fall into

  1. Blue and green get reversed on taxiway lighting. Taxiway edge lights are blue, while green taxiway lights are centerline lights. Runway edge lights are white, and on an instrument runway the final section is amber as a caution zone, which candidates often misread as a taxiway color instead.
  2. A flashing red light gun signal is treated as one signal with one meaning. On the ground it means taxi clear of the runway in use; to an aircraft in flight it means the airport is unsafe and do not land. Several test questions turn entirely on whether the aircraft is airborne or on the ground.
  3. Candidates still call 121.5 megahertz the primary distress frequency of a modern ELT. Satellites no longer monitor 121.5 megahertz for alerting. A current unit sends its coded digital alert on 406 megahertz and uses 121.5 megahertz only as the homing signal that search crews track on scene.

7 free sample questions from ACS AM.II.I

  1. AM.II.ITap an answer

    What does a flashing red light signal from the control tower mean to an aircraft operating on the ground?

  2. AM.II.ITap an answer

    When installing or troubleshooting a VHF communications antenna, why is the bonding of the antenna base to the aircraft structure important?

  3. AM.II.ITap an answer

    What is the primary purpose of an emergency locator transmitter (ELT) installed in an aircraft?

  4. AM.II.ITap an answer

    Modern ELTs required for civil aircraft transmit their primary digital distress signal on which frequency?

  5. AM.II.ITap an answer

    Along the edges of a runway, the standard FAA runway edge lighting normally displays what color to a pilot during the landing approach and rollout?

  6. AM.II.ITap an answer

    On a runway equipped with edge lighting, what color do the runway threshold lights display to a pilot approaching to land?

  7. AM.II.ITap an answer

    What color are the edge lights used to outline a taxiway, as distinguished from the lights used to outline a runway?

What does a flashing red light signal from the control tower mean to an aircraft operating on the ground?

ACS code: AM.II.I

Correct answer: Taxi clear of the runway in use

Rationale: In the FAA light-gun signal system, a flashing red light directed at a ground aircraft means 'taxi clear of the runway in use.' A steady red means stop, a flashing white means return to starting point on the airport, and a flashing green means cleared to taxi. These signals are the standard backup for radio communication failure.

When installing or troubleshooting a VHF communications antenna, why is the bonding of the antenna base to the aircraft structure important?

ACS code: AM.II.I

Correct answer: It provides a proper ground plane for the antenna

Rationale: A VHF antenna requires a low-resistance bond to the metal skin so the airframe acts as the ground plane that the antenna radiates against. Poor bonding raises resistance, degrades the radiation pattern, and causes weak transmission and reception. Bonding does not increase transmitter power or change the operating frequency.

What is the primary purpose of an emergency locator transmitter (ELT) installed in an aircraft?

ACS code: AM.II.I

Correct answer: Transmit a signal to aid search and rescue after a crash

Rationale: An ELT automatically transmits a distress signal on designated emergency frequencies to help search-and-rescue forces locate an aircraft after an accident; it is activated by the impact forces of a crash or manually. It is not a two-way voice radio and does not provide cockpit navigation displays.

Modern ELTs required for civil aircraft transmit their primary digital distress signal on which frequency?

ACS code: AM.II.I

Correct answer: 406 MHz

Rationale: Current ELTs transmit a digital distress signal on 406 MHz, which is monitored by the satellite-based search-and-rescue system and can carry a coded aircraft identifier for accurate location. The older 121.5 MHz signal is now used only as a low-power homing aid, and 243.0 MHz is a military frequency. The 406 MHz signal greatly improves location accuracy.

Along the edges of a runway, the standard FAA runway edge lighting normally displays what color to a pilot during the landing approach and rollout?

ACS code: AM.II.I

Correct answer: White

Rationale: Standard runway edge lights are white, marking the lateral limits of the usable runway surface. Blue lights mark taxiway edges, and green lights mark runway thresholds (when viewed from the approach end). Knowing the color code helps the mechanic verify that the correct lamps and lenses are installed during airfield-lighting maintenance references.

On a runway equipped with edge lighting, what color do the runway threshold lights display to a pilot approaching to land?

ACS code: AM.II.I

Correct answer: Green

Rationale: Threshold lights show green to an aircraft on approach, marking the beginning of the runway available for landing; the same fixtures appear red to traffic on the runway looking back, marking the end of the usable surface. Runway edge lights are white and taxiway edge lights are blue. This color logic is part of standard airport lighting conventions.

What color are the edge lights used to outline a taxiway, as distinguished from the lights used to outline a runway?

ACS code: AM.II.I

Correct answer: Blue

Rationale: Taxiway edge lights are blue, which distinguishes the taxi routes from the white edge lights of the runway. Some taxiway centerlines use green lights, but the edge lights are blue. This consistent color coding lets pilots and ground crews tell runways from taxiways at night and lets mechanics confirm correct lens colors during lighting maintenance.

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Frequently asked questions

What does a flashing red light from the control tower mean?
It depends on where the aircraft is. To an aircraft on the ground, flashing red means taxi clear of the runway in use. To an aircraft in flight, flashing red means the airport is unsafe and the pilot should not land. Steady red means stop for an aircraft on the ground, and means continue circling and give way to other aircraft for one in flight.
What color are taxiway lights compared with runway lights?
Taxiway edge lights are blue and taxiway centerline lights are green. Runway edge lights are white, and on an instrument runway the last portion of the runway shows amber to a departing pilot as a caution zone. Threshold lights appear green to an aircraft approaching to land and red when seen from the runway side as runway end lights.
What frequency does an ELT transmit on?
A modern emergency locator transmitter broadcasts a coded digital distress message on 406 megahertz, which satellites receive and pass to search and rescue along with the beacon's registration identity. The same unit transmits a lower-power analog signal on 121.5 megahertz that search crews and aircraft use to home in on the beacon during the final stage of a search.
Why does a VHF antenna have to be bonded to the airframe?
The skin under a blade or whip antenna acts as the ground plane and the return path for radio frequency current, so the antenna base needs a clean, low-resistance, metal-to-metal connection to structure. Poor bonding weakens transmission, distorts the radiation pattern, raises standing wave ratio, and lets precipitation static and electrical noise into the receiver as interference.
What is a frequency of 112.1 MHz used for?
That frequency falls in the VHF navigation band of roughly 108 to 118 megahertz, which is assigned to VOR stations and, in its lower portion, to instrument landing system localizers. VHF communication radios operate above it, starting at 118 megahertz. Recognizing which band a given frequency belongs to is a common written-test question in this subject area.

All 40 ACS areas

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Airframe

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Primary sources

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