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Avionics Operational Test Standards

FS/OAS A-24

Revision F

September 10, 2018

The following standards apply to all contractually required/offered avionics equipment 

under US Forest Service contracts and Department of the Interior interagency fire 

contracts.

Abbreviations and Selected Definitions are in Section 7. 

1. Communications Systems

Interference

No squelch breaks or interference with other transceivers with 1 MHz separation. No 

transmit interlock functions for communications transceivers on fire aircraft.

VHF-AM Transceiver

Type TSO approved, selectable frequencies in 25 kHz increments, 760 

channel minimum, operation from 118.000 to 136.975 MHz, 720 

channel acceptable for DOI if contractually permitted

Display Visible in direct sunlight

Operation To and from service monitor

Transmitter System modulation from 50% to 95% and clear, 5 watts minimum 

output power, frequency within 20 PPM (+2.46 kHz @ 122.925 MHz) 

(47 CFR 87.133)

Receiver

(All Aircraft)

Squelch opens when receiving a signal from 50 Nautical Miles or 

greater when no other radios on the aircraft are transmitting. (See 

FS/OAS A-30 Radio Interference Test Procedures)

Receiver

(Fire aircraft approved 

for passengers or aircraft 

requiring two pilots)

Squelch opens when receiving a signal from 24 Nautical Miles or 

greater while other radios on the aircraft are transmitting with a 

spacing of 2 MHz or greater. (See FS/OAS A-30 Radio Interference 

Test Procedures)
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Aeronautical VHF-FM Transceiver (P25 required for Fire)

Type Listed on Approved Radios list, P25 meets FS/AMD A-19

Power Output 10 watts nominal output, multiband transceivers 6 to 10 watts

nominal output

Antenna Cobham (Comant) CI 177-1 or equivalent

CTCSS Tones All current TIA-603 standard tone encode & decode tone capability,

TX tone level of 300 to 600 Hz in narrowband, frequency within 1.5 

Hz of selected tone, proper operation

NAC and TGID (P25) Operator selectable

All Transmitters Narrowband deviation from 1.5 to 2.5 kHz, narrowband frequency

within 2.5 PPM (+421 Hz @ 168.3500 MHz) (per NTIA Manual

Chapter 5)

Guard Transmitter Quickly selectable, operates on 168.6250 MHz, TX CTCSS tone of 110.9 

Hz

All Receivers Squelch opens when receiving a signal from 50 Nautical Miles or 

greater when no other radios on the aircraft are transmitting. (See 

FS/OAS A-30 Radio Interference Test Procedures), audio output of at 

least 100 mV with narrowband input, less than 10% distortion

All Receivers

(Fire aircraft approved 

for passengers or aircraft 

requiring two pilots)

Squelch opens when receiving a signal from 24 Nautical Miles or 

greater while other radios on the aircraft are transmitting with a 

spacing of 2 MHz or greater. (See FS/OAS A-30 Radio Interference 

Test Procedures)

Guard Receiver

(Fire Aircraft)

Independent receiver, operates on 168.6250 MHz, cannot scan Guard, 

capability to enable/disable CTCSS tone of 110.9

Mounting Meets AC 43.13-2B, controls equally convenient to PIC and

SIC/observer

AUX-FM Provisions

Operation RX & TX functions through aircraft audio system(s), sidetone present,

TX deviation output matches portable’s stand-alone output, installed 

per FS/AMD A-17

Controls TX and RX selectors on all required audio controls

Antenna Cobham (Comant) CI 177-1 or equivalent
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Mounting Facilities Meeting AC 43.13-2B (Field Support Services AUX-EPH-RB or 

equivalent), within 18” of AUX-FM connectors, controls convenient to

SIC/observer

Connectors MS3112E12-10S, female BNC, both bulkhead mounted, both adjacent 

to each other

VHF-FM Programming Port

Operation Location, ability to program each radio

Adapters Available for installed radio type, serial or USB connector

VHF-FM Aeronautical Antenna: Light Fixed Wing

RF Cable Location, cable length, male BNC connector

Antenna Cobham (Comant) CI 177-1 or equivalent

P25 Digital VHF-FM Mobile Radio

Type Listed on Approved Radios list

Operational Check Proper RX and TX operation

Power Output 30 watts minimum nominal output

Antenna Antenna Specialists ASPR-7490; Maxrad MWB-5803; or equivalent

CTCSS Tones All current TIA-603 standard tone encode & decode tone capability,

TX tone level of 300 to 600 Hz in narrowband, frequency within 1.5 

Hz of selected tone, proper operation

NAC and TGID Operator selectable via radio controls

Receiver Squelch opens @ 0.25 to 0.5 uV with direct connection at 138, 156,

and 173.975 MHz, audio output of at least 100 mV with narrowband 

input (1.5 to 2.5 kHz modulation), less than 10% distortion

Transmitter Narrowband deviation from 1.5 to 2.5 kHz, narrowband frequency 

within 2.5 PPM (+421 Hz @ 168.3500 MHz) (per NTIA Manual

Chapter 5)

Field Programmability Contractor demonstration without the use of a computer to program

the radio
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P25 Digital VHF-FM Portable Radio

Type Listed on Approved Radios list

Operational Check Proper RX and TX operation

Power Output 1 watt but no more than 10 watts nominal output

Battery Alkaline: At least one clamshell; Rechargeable: Two fully charged

battery packs at beginning of each shift

CTCSS Tones All current TIA-603 standard tone encode & decode tone capability, 

TX tone level of 300 to 600 Hz in narrowband, frequency within 1.5

Hz of selected tone, proper operation

NAC and TGID Operator selectable via radio controls

Receiver Squelch opens @ 0.25 to 0.5 uV with direct connection at 138, 156, 

and 173.975 MHz, audio output of at least 100 mV with narrowband

input (1.5 to 2.5 kHz modulation), less than 10% distortion

Transmitter Narrowband deviation from 1.5 to 2.5 kHz, narrowband frequency

within 2.5 PPM (+421 Hz @ 168.3500 MHz) (per NTIA Manual

Chapter 5)

Field Programmability Contractor demonstration without the use of a computer to program

the radio

Public Address Systems

Controls Operated through each required aircraft audio control systems, uses 

headset/helmet mic

Siren Provides Yelp and Wail tones activated by PIC and SIC/observer

External External speakers, easily heard 100 feet below aircraft in flight

Internal Internal speakers, easily heard throughout the passenger 

compartment while in flight, Smokejumper A/C less than 10% 

distortion for conveying intelligible messages to all occupants from 

all positions with jump door open, (system required on A/C with +19 

PAX seats per 14 CFR 135.150 & Smokejumper A/C)
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2. Audio Systems

Audio Control System: General Requirements Applicable to Each Required System

Location Convenient to required operator(s), not a safety hazard

Labeling Legible, permanent, understandable (i.e. COM 1, COM 2, FM 1, AUX, 

etc or COM 1, COM 2, COM 3, COM 4, etc with radios marked 

accordingly)

Hum, Noise, and 

Crosstalk

40 dB below specified audio output

Specified Audio Output 100 mW with an input of 250 mV, both at 600 ohms

Distortion Less than 10%

TX Selection Automatically selects proper radio and companion receiver; each 

required transceiver and PA has separate TX position

RX Selection Selects proper radio receiver (on/off switch)

PTT Switch Proper operation, non-pilot switches not on flight controls

ICS and Radio RX Volume Proper operation, audio level

Sidetone Present for each transceiver, acceptable audio level

Audio Control System: Helicopter: See applicable drawings

Required Controls Individual RX selection of each radio, separate master RX and ICS 

audio level controls

RX Selection Each required receiver has individual RX selector independent of the 

transmitter selector

PTT Switch Separate radio TX and ICS TX switches at all required positions

Rappel/EU Proper ICS and TX capability at specified positions, additional Audio 

Control System per contracts and drawings

Audio Control System: Air Tactical Type 1 & 2

Required Controls Dual systems with individual RX selection of each radio

ATGS Instructor TX/RX operation uses SIC/observer audio control or has a separate 

system (Nav audio not required for Instructor system)
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Audio Control System: Airtanker

Required Controls PIC and SIC systems interchangeable, individual RX selection of each 

radio, pilot inspector monitors SIC or has a separate system (no TX or 

NAV required for inspector)

Audio Control System: Smokejumper

Required Controls Individual RX selection of each radio, separate master RX and ICS 

audio level controls

ICS and Radio RX Volume Audio level sufficient for intelligible reception to helmeted spotter 

with jump door open while in flight

Intercommunications System (ICS)

Required Positions Per contractually required locations

Operation Proper audio & mic operation at each required position, 

Smokejumper isolation with Call button and PIC annunciator

Hot Mic/VOX Presence per contract requirements, proper operation

PTT and Volume Controls Presence per contract requirements, proper operation, Airtanker ICS 

PTT not required if normal conversation can be maintained while in

flight

3. Navigation Systems

Global Positioning Systems (GPS): All

Installation Convenient to both PIC and SIC/Observer

Operation Correct present position or lock on, database age does not exceed

contract limit, WGS-84 datum, degrees/decimal degrees display

Moving Map

(when required)

Display area 1.5” high x 3.0” wide minimum, aircraft position relative

to waypoints, displays geographical features

Data Connector (when 

required)

DB-9F connector, correct pins active, proper location

Aeronautical GPS

Type TSO approved, panel mounted, IFR installation requires Flight Manual 

documentation
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Portable GPS

Type Aviation portable, not a drive along the road type

Installation Meets AC 43.13-2B, operates using aircraft power

Antenna Antenna remoted from unit with clear path to satellite signals

Additional GPS Antenna

Type TSO approved, compatible with the portable GPS of the requesting 

unit

VOR

Type TSO approved, panel mounted

Operation Display visible in direct sunlight, audio, flag pull, to/from operation

Bearing Error ±3° maximum (usually 11⁄2 out of 5 dots) or meeting the 

manufacturer’s specifications (whichever is more stringent), 

maximum variation between dual system of +40 (usually 2 out of 5 

dots), IFR aircraft require aircraft log/record entry for IFR 30 day 

check per 14 CFR 91.171

Localizer and Glideslope

Type TSO approved, flag pull, proper deviation direction, interfaced to the 

correct navigation system

Deviation Error .07% maximum (approximately 1 needle width) or meeting the 

manufacturer’s specifications (whichever is more stringent)

Marker Beacon

Type TSO approved, three light

Operation All indicators operate properly, acceptable sensitivity, acceptable 

audio level (service monitor required)

DME

Type TSO approved, independent from GPS unless IFR GPS is allowed to 

replace DME by contract

Operation Display visible in direct sunlight, proper distance to station

ADF

Operation Display visible in direct sunlight, points to station, 360° operation, 

acceptable audio
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4. Surveillance Systems

Emergency Locator Transmitter (ELT)

Type TSO-C91a or newer (DOI requires TSO-C126 or newer for most 

contracts)

Mounting Per TSO and manufacturer’s instructions (deflection less than 0.1” 

with 100 lbs. of force applied)

Antenna Mounted externally to the aircraft unless installed in a location 

approved by the aircraft manufacturer, portable antenna available for 

automatic portable types

Battery Date Not expired, date marked on ELT which matches aircraft records

Operation Direct connection to ELT required if operating outside of the first five 

minutes of the hour, use test function if available, manually operates, 

PRF acceptable, buzzer activates for 406 MHz models

Remote Location visible and accessible to PIC, functionality, indicator

Logbook Annual 14 CFR 91.207(d) test completed

Registration 

(for TSO-C126)

Currently registered with national authority (NOAA in USA)

TSO-C126 Transmissions Hex code matches registration document, correct country code, 

correct aircraft registration number (if transmitted)

Automated Flight Following (AFF)

Operation Current position data displayed on aff.gov, required data is accurate

Installation Per manufacture’s manual and AC 43.13-2B, operates using aircraft

power, dedicated circuit breaker

Antenna External to unit, clear path to satellites

Additional Telemetry Unit (ATU)

Operation Reports required data through AFF, correct data confirmed by USFS 

AFF program

Installation Per manufacture’s manual and AC 43.13-2B, operates using aircraft

Power,
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Bucket Operations Bucket provides ground to ATU without action beyond connecting the 

bucket to aircraft or longline

Transponder

Type TSO-C74b, TSO-C74c (Mode A/C) or TSO-C112 (Mode-S)

Installation Meets 14 CFR 91.215(a), 91.215(b), and 91.413

Records Required 14 CFR 91.413 & 14 CFR Part 43 Appendix F logbook entry

not expired (24 calendar month maximum)

Altimeter and Automatic Pressure Altitude Reporting systems

Installation Maintained to 14 CFR Part 91 IFR requirements

Records 14 CFR 91.411 & 14 CFR Part 43 Appendixes E and F logbook entry 

not expired (24 calendar month maximum)

Traffic Advisory System (TAS)

Type TSO approved active system. Maximum range at least 10 NM, TCAS 

required on turbine airplanes with +10 PAX seats per 14 CFR 135.180

Display Within view of PIC and SIC, traffic displayed graphically, range 

selection of 2 miles or less unless the 2 mile display area has a 

diameter of 2.75 inches or larger (ASM requires 1 NM display range)

Operation On and operating per 14 CFR 91.221, coverage in all directions above 

and below aircraft,

Automatic Dependent Surveillance – Broadcast Out (ADS-B OUT)

Type Approved to TSO-C154c (UAT) or TSO-C166b (1090ES) (TSO-C166b 

required outside of the United States)

5. General Systems

Autopilot

Operation Capable of operating the aircraft controls to maintain flight and 

maneuver it about the three axes

Auxiliary Power Source (3 Pin)

Connector MS3112E12-3S installed, proper location, permanently mounted, 

polarity, voltage at correct pins

Circuit Breaker Correct amperage value, operation
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Bucket/Torch Connector (9 Pin)

Connector MS3101A24-11S installed, within 12” of cargo hook, securing lanyard 

or fixed to aircraft structure

Wiring Pin D = ground, Pin E = switched 28V, Pin G = bucket connected (Pin G 

only required for ATU)

Circuit Breaker 50 ampere, operation

Cargo Bell and Light System: Smokejumper

Cargo Bell Location, activation, sound level

Light System Location, activation, indicators

Cockpit Voice Recorder

Type TSO approved, (required on multiengine turbine powered A/C with 

+6 PAX seats requiring two pilots by TC or operating rule per 14 CFR 

91.609 and 135.151)

Operation Proper area mic location, headset mic(s) operation, radio RX 

operation, locator beacon battery date current

Magnetic Direction Indicator (Compass)

Installation Placarded and legible, calibrated with engines operating stating that 

radios were on or off, calibration readings of not more than 300 

increments (normal category airplanes, airtankers and 

smokejumpers) or 450 increments (all others), Errors within 10°, 

compass swing required after installation of new avionics systems

Multi-Function Display (MFD)

Operation In view of PIC, GPS navigation displayed on color moving map, 

Displays TAS and weather datalink when installed

Radar Altimeter

Operation 0-2000 feet AGL, altitude low (DH) light in PIC’s primary field of view, 

DH is adjustable

Terrain Awareness and Warning System (TAWS)

Type Approved to TSO-C151 (required on turbine powered airplanes with 

+6 PAX seats per 14 CFR 91.223 and 135.154), Flight Manual 

documentation

Operation Acceptable audio, disabled on Smokejumper and paracargo 

operations
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USB Ports

Type TSO approved, dual ports at each position

Installation Proper location, circuit breaker size, access 

Operation Proper voltage, proper current (by contract but not less than 2A per 

port)

6. Installation and Maintenance

General

Strict adherence to the guidelines in FAA AC 43.13-1B and AC 43.13-2B

Visual Inspection

Inspect for obvious damage, inoperative displays, missing or incorrect parts, proper labeling, 

and documentation

Antennas

Type Broadband aircraft antennas covering the proper frequency band for 

the interfaced system

Installation Rigidity, doubling plates, proper bonding, proper RF cables, security, 

proper wire size, condition, not painted (except OEM), no corrosion, 

no unauthorized repairs

VSWR 3.0:1 or better

Wiring

Correct type, no chafing/rubbing, properly secured, properly terminated, condition

7. Abbreviations & Selected Definitions

AC Advisory Circular

A/C Aircraft

ADF Automatic Direction Finder

ADS-B Automatic Dependent Surveillance - Broadcast

AFF Automated Flight Following
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AM Amplitude Modulation

AMD Aviation Management Directorate (Changed to OAS)

ATGS Air Tactical Group Supervisor

ATU Additional Telemetry Unit

AUX-FM Auxiliary Frequency Modulated portable radio

BNC Bayonet Neill Concelman, a quick disconnect RF connector

CFR Code of Federal Regulations

CTCSS Continuous Tone Controlled Squelch System

CVR Cockpit Voice Recorder

dB Decibel

DME Distance Measuring Equipment

DOI Department of the Interior

ELT Emergency Locator Transmitter

FDR Flight Data Recorder

FM Frequency Modulation

FS Forest Service

GPS Global Positioning System

GPWS Ground Proximity Warning System, see TAWS

GS Glideslope, see ILS

Hz Hertz (1 hertz)

ICS Intercommunication System
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IFR Instrument Flight Rules

ILS Instrument Landing System, see GS and LOC

kHz Kilohertz (1,000 hertz)

LOC Localizer, see ILS

MB Marker Beacon

MEL Minimum Equipment List

MFD Multifunction Display

Mic or mic Microphone

MHz Megahertz (1,000,000 hertz)

Multiband Transceiver A transceiver capable of operating in more than one frequency band 

(i.e. 136 to 174 MHz and 403 to 512 MHz) as opposed to a standard 

VHF-FM transceiver which can only operate in the 136 to 174 MHz 

frequency band.

mW Milliwatts (0.001 watts)

mV Millivolts (0.001 volts)

NAC Network Access Code, see P25

NAV Navigation Systems

NM Nautical Mile

NTIA Manual National Telecommunications & Information Administration, Manual

of Regulations and Procedures for Federal Radio Frequency

Management

NTE Not To Exceed

OAS Office of Aviation Services

P25 Project 25 Digital, open architecture digital communications system

PA Public Address
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PAX Passenger or passengers

PIC Pilot in Command

PPM Parts Per Million

PRF Pulse Repetition Frequency

PTT Push to Talk

RF Radio Frequency

Rx or RX Receive or reception

SIC Second in Command, copilot

TAS Traffic Advisory System

TAWS Terrain Awareness and Warning System

TC Type Certificate

TCAD Traffic Collision Alert Device, passive system, does not meet TAS 

contract requirements

TCAS Traffic Collision Avoidance System, subset of TAS 

TGID Talkgroup, a sub code of a NAC

TIS

(Now TIS-A)

Traffic Information Service, obsolete passive traffic system, 

operational within 55 NM of specially enabled radar sites which are 

being decommissioned, does not meet TAS contract requirements

TIS-B Traffic Information Service – Broadcast, passive traffic provided to

ADS-B IN systems from ground stations, does not meet TAS contract 

requirements

Transmit Interlock A function that reduces receiver sensitivity when other radios on the 

aircraft are transmitting

TSO Technical Standard Order

Tx or TX Transmit or transmission
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USB Universal Serial Bus

uV Microvolt (0.000001 volts)

VHF Very High Frequency

VOR VHF Omnidirectional Range

VOX Voice Activated

VSWR Voltage Standing Wave Ratio