Advisory 

Circular

 

Subject: Operational Authorization 

Process for use of Data Link 

Communication System

Date: 12/29/05

Initiated by: AFS-430 

AC No: 120-70A 

 This advisory circular (AC) presents various methods for operators of differing data link systems 

to meet international standards set by the International Civil Aviation Organization (ICAO) and 

the Regional Airspace Authorities. The FAA notes that there is presently no requirement in Title 

14 of the Code of Federal Regulations to have data link communications when operating in the 

National Airspace System (NAS). Instead, the regulations in Title 14 govern radio 

communication systems, and nothing in this AC absolves an operator from the requirement to 

have and use a voice communication system when operating in the NAS. However, operators 

that choose to use a data link system (in addition to the required voice communication system) 

must obtain FAA design approval and a revision to their Operating Specifications. Thus, the 

FAA is issuing this AC is to present the consensus of the aviation community regarding 

acceptable methods, procedures, and training for users of data link systems. 

ORIGINAL SIGNED BY 

Carol Giles for 

James J. Ballough 

Director, Flight Standards Service 

 

12/29/05 AC 120-70A 

CONTENTS

 Page 

1. Purpose.................................................................................................................................1 

2. Cancellation .........................................................................................................................1 

3. Applicability ........................................................................................................................1 

4. Related Material...................................................................................................................2 

5. How To Order......................................................................................................................3 

6. Background And Definitions...............................................................................................3 

7. Authorization To Use Data link Communications In Flight Operations.............................8 

8. Flightcrew Qualification For Use Of Data link Communications.....................................10 

9. Other Operational Issues....................................................................................................16 

10. Maintenance.......................................................................................................................17 

11. Data link Communications Operational Use .....................................................................18 

12. Data Link Event Reporting ................................................................................................20

13. Foreign Air Carriers...........................................................................................................21 

APPENDIX 1 SAMPLE DATA LINK EVENT REPORTING INFORMATION (1 page)................ 1 

APPENDIX 2. DATA LINK COMMUNICATIONS MINIMUM REQUIREMENT 

 LIST (MEL) AND MASTER MINIMUM EQUIPMENT LIST (MMEL) 

 PROVISIONS (2 pages).................................................................................................... 1 

APPENDIX 3. PART 129 PROVISIONS FOR USE OF DATA LINK 

 IN U.S. AIRSPACE (1 page)............................................................................................ 1 

APPENDIX 4. ACRONYMS AND ABBREVIATIONS (2 pages) ......................................................... 1

Page i (and ii) 

12/29/05 AC 120-70A 

1. PURPOSE. This advisory circular (AC) presents various methods for operators of differing 

data link systems to meet international standards set by the International Civil Aviation 

Organization (ICAO) and the Regional Airspace Authorities. The FAA notes that there is 

presently no requirement in Title 14 of the Code of Federal Regulations to have data link 

communications when operating in the National Airspace System (NAS). Instead, the 

regulations in Title 14 govern radio communication systems, and nothing in this AC absolves an 

operator from the requirement to have and use a voice communication system when operating in 

the NAS. However, operators that choose to use a data link system (in addition to the required 

voice communication system) must obtain FAA design approval and a revision to their 

Operating Specifications. Thus, the FAA is issuing this AC is to present the consensus of the 

aviation community regarding acceptable methods, procedures, and training for users of data link 

systems. 

The original advisory circular, AC 120-70, was applicable to Aeronautical Telecommunication 

Network (ATN) VHF Data Link (VDL) Mode 2 communication systems. The Future Air 

Navigation System (FANS 1/A) system used in Oceanic and Remote airspace is an analog 

system which communicates over Aircraft Communications Addressing and Reporting System

(ACARS). Guidance is needed for the operation of both systems and therefore the requirement 

for this revision. 

2. CANCELLATION. AC 120-70 dated February 17, 2000, Initial Air Carrier Operational 

Approval for Use of Digital Communication System, is cancelled. 

3. APPLICABILITY. This AC applies to aircraft and air carriers operating under parts 121, 

and 135, other organizations conducting training approved in accordance with part 121 (e.g., 

training centers or aircraft manufacturers), operators under part 125, and foreign air carriers 

conducting operations in United States airspace under part 129. This AC describes the process 

for obtaining operational authorization for data link communication systems, acceptable methods 

for training and maintenance, and operational policies for use. In addition, it describes 

appropriate actions in the event of an exceptional air traffic control (ATC) data link 

communications event, and criteria for foreign operator use of data link communications in U.S. 

airspace. This AC may be applied to operators conducting operations under 14 CFR part 91. 

This AC does not address the use of data link communications for specific ATS applications 

such as ATIS, PDC, and DDTC, which are information services not directly related to aircraft 

separation. 

The Data Link System should comply with International Standards and Recommended Practices 

and Procedures for Air Navigation Services, Annex 10 to the Convention on International Civil 

Aviation, Aeronautical Telecommunications, Volume II, Communications Procedures including 

those with PANS status, Chapter 8, Aeronautical Mobile Service – Data Link Communications, 

Sixth Edition October 2001. This AC is consistent with-Volume III, Part I, Digital 

Communication Systems, Chapter 3, Aeronautical Telecommunication Network (ATN).

Par 1 Page 1 
AC 120-70A 12/29/05 

4. RELATED MATERIAL. 

a. Title 14 Code of Federal Regulations (14 CFR). The following 14 CFR parts are 

applicable to the communications systems and applications covered in this document: parts 21, 

23, 25, 27, 29, 43, 91, 121, 125, 129 and 135. 

b. Advisory Circulars. The following AC provides additional information that may assist 

in the operational authorization of data link communications systems: 

• AC 20-140, Guidelines for Design Approval of Aircraft Data Communications 

Systems 

c. International Civil Aviation Organization (ICAO) documents: 

 (1) Annex 10 to the ICAO Convention (Standards and Recommended Practices – 

SARP’s), Volume III, Part 1, Data link Data Communications Systems. 

 (2) Document 4444 (PANS/ATM), Procedures for Air Navigation Services - Rules of 

the Air and Air Traffic Services. 

 (3) Annex 6 to the ICAO Convention Operations of Aircraft.

 (4) Annex 11 to the ICAO Convention Air Traffic Services.

 (5) Document 7030, Regional Supplementary Procedures. 

d. FAN’s Interoperability Team and FAN’s Interoperability Group Global Document: 

• FAN’s Operations Manual 

e. The following RTCA documents are available from RTCA Inc., 1140 Connecticut 

Avenue, NW. Suite 1020, Washington, DC 20036: 

 (1) DO-210C, Minimum Operational Performance Standards for Aeronautical Mobile 

Satellite Service (AMSS avionics). 

 (2) DO-212, Minimum Operational Performance Standards for Airborne Automatic 

Dependent Surveillance (ADS) Equipment. 

 (3) DO-215A, Guidance on Aeronautical Mobile Satellite Service (AMSS) End-to-End 

System Performance. 

 (4) DO-219, Minimum Operational Performance Standards for ATC Two-Way Data 

Link Communications (Applications). 

 (5) DO-224, Signal-in-Space Minimum Aviation System Performance Standards for 

Advanced VHF Data link Communications. 

Page 2 Par 4 
12/29/05 AC 120-70A 

 (6) DO-231, Design Guidelines and Recommended Standards for the Internet working, 

Implementation and Use of AMS(R)S. 

 (7) DO-239, Minimum Operational Performance Standards for Traffic Information 

Services (TIS) Data Link Communications. 

 (8) DO-240, Minimum Operating Performance Standards for Aeronautical 

Telecommunication Network (ATN) Avionics. 

 (9) DO-242, Minimum Aviation System Performance Standards for Automatic 

Dependent Surveillance Broadcast (ADS-B). 

 (10) DO-243, Guidance for Initial Implementation of Cockpit Display of Traffic 

Information. 

 (11) DO 264, Guidelines for Approval of the Provision and Use of Air Traffic Services 

Supported by Data Communications. 

f. The following SAE documents are available from SAE International, Customer 

Sales, 400 Commonwealth Avenue, Warrendale, PA, 15096: 

 (1) ARP 4754, Certification Considerations for Highly-Integrated or Complex Aircraft 

Systems. 

 (2) ARP 4761, Guidelines and Methods for Conducting the Safety Assessment Process 

on Civil Airborne Systems and Equipment. 

5. HOW TO ORDER.

 a. A copy of this AC and other ACs mentioned herein may be obtained from: 

U.S. Department of Transportation 

Subsequent Distribution Office, SVC-121.23 

Ardmore East Business Center 

3341 Q 75th Ave 

Landover, MD 20785 

 b. Identify this publication in your order as Federal Aviation Administration (FAA) 

Advisory Circular (AC 120-70A), Operational Authorization Process For Use Of Data link 

Communication Systems. 

6. BACKGROUND AND DEFINITIONS. 

a. Data Link Implementation. Data link applications are being implemented in flight 

operations and other operations on a widespread basis (e.g., PDC, D-ATIS, FANS-1 CPDLC, 

FIS/TIS, and ADS). Data link applications operate without any specific knowledge by the user 

as to whether a satellite, VHF, or HF air/ground data link medium network service is in use. 

However, these applications may be limited by the level of end-to-end data link service 

Par 4 Page 3 
AC 120-70A 12/29/05 

implementation in use. (e.g., ACARS, FANS-1 ACARS/ARINC 622, CNS/ATM-1). This AC 

provides information for U.S. operators, aircraft and data link manufacturers, various inspectors, 

foreign air carriers operating in U.S. airspace, and other aviation organizations regarding a 

means acceptable to the FAA for the use of data link systems in ATS communications. This 

information is intended to facilitate the operational authorization of data link systems, promote 

timely and comprehensive program implementation, encourage development of standard 

practices for the application of data link techniques, and provide an appropriate response to 

exceptional data link events. 

 b. Definitions. Certain definitions in this AC are taken from other FAA materials. Other 

definitions are unique to this AC, and their application is limited to use with data link systems. 

(1) Aircraft Certification Office (ACO). FAA offices responsible for the 

determination of aircraft airworthiness and other issues related to parts 21, 23, 25, 33, and other 

airworthiness rules. ACOs issue Type Certificates (TC), and Supplemental Type Certificates 

(STC), and are responsible for the technical assessment of service difficulties and Airworthiness 

Directives (AD). 

(2) Aircraft Evaluation Group (AEG). FAA offices responsible for operational 

aspects of newly certificated, modified, or "in-service" aircraft. AEGs establish FAA criteria for 

pilot qualification as it relates to Flight Standardization Board (FSB) and initial aircraft

certification, AEGs are also responsible for minimum equipment lists (MEL), initial airworthiness, and other operationally related regulation, including 14 CFR parts 43, 61, 91, 121, 135. 

(3) Certificate-Holding District Office (CHDO). A Flight Standards office 

responsible for the administration of part 119 certificate authority for operations conducted under 

parts 121 or 135 for a particular certificate holder. 

 (4) Air Traffic Data Link Service. A data communication capability comprising 

air/ground and ground/ground data network services, specified data link message sets and 

protocols, aircraft equipment, ATS Facility equipment, and operational procedures intended to 

provide primary or supplemental ATS communications without reversion to voice procedures 

under most circumstances. 

 (5) Data Link Event. For the purpose of this AC, a Data Link Event is one or more of 

the following occurrences or situations related to data link: 

• In-flight traffic conflicts or potential conflicts as determined by a flightcrew 

member in which use of a data link service is suspected to be contributing cause. 

• Near mid-air collisions (NMAC) in which the use of a data link service is 

suspected to be a contributing cause. 

• Data link system performance below that of normal operation. 

• ATC operational error involving a data link-equipped aircraft. 

Page 4 Par 6 
12/29/05 AC 120-70A 

• Other occurrences or situations in which use of a data link service is suspected to 

compromise continued operational safety. Loss of standard ATC separation 

resulting from a procedure or maneuver where a data link transaction, failure, or 

unmonitored error is suspected to be a factor. 

• Use of the data link service that caused excessive crew workload. 

• A data link service that provides reasonable information but is subsequently 

verified to be erroneous. 

• An excursion of more than 500 feet from an assigned flight level/altitude, or a 

lateral/longitudinal deviation exceeding ATS minimum separation criteria in 

which use of a data link service is suspected to be a contributing cause. 

 (6) Data Link Service Academic Training (as applied within this AC). Training that 

exclusively addresses knowledge requirements (rather than skills), and is usually related to 

achieving satisfactory knowledge of data link service concepts, systems, limitations, or 

procedures. The academic training on data link services is generally accomplished using a 

combination of classroom methods (stand up instruction, slide/tapes, computer-based instruction 

(CBI), tutorial, etc.), flight manual information, bulletins, or self-study. See paragraph 8b for an 

expanded explanation of the recommended curriculum. 

 (7) Data Link Service Use Training. This is training that addresses all of the skills 

related to the operational use of data link services including the knowledge and skills needed to 

receive information provided by data link services, and appropriately accept, reject, cancel, or 

defer a response to that information. In addition, this training includes the knowledge and skills 

needed to load, store, formulate, and request information from the data link service. 

 (8) Data Link System. A general term referring to data link digital or analog based 

systems. At the present time the digital operation is known as VDL–Mode 2 system. The analog 

operation is known as the FANS system. The FANS (1/A) system uses both digital and analog 

components. The data link applications are digital and binary encoded, and then processed by 

the ACARS convergence function (ACF) for transmission over a character-oriented network. 

 (9) Flight Standards District Office (FSDO). An FAA field office serving an assigned 

geographical area and staffed with Flight Standards personnel who serve the aviation industry 

and the general public on matters relating to the licensing of aviation personnel, certification of 

aircraft and operational authorization of air carriers, commuter and general aviation operations. 

 (10) Flight Standards Board (FSB). The FAA board responsible for establishing or 

revising crew qualification requirements (e.g., training, checking, currency, and type rating(s))

for specific aircraft). FSBs are established for each large turbojet and turboprop aircraft type 

used in air transportation, as well as other part 25 aircraft, transport category multi-engine 

helicopters, and large multi-engine piston aircraft. 

Par 6 Page 5 
AC 120-70A 12/29/05 

 (11) Follow-on STC (as related to data link communications). A data link 

communications STC other than as described in item (13) below for an "Initial TC/STC." The 

following examples are considered to be "follow-on" STCs: 

• A previously approved data link communications installation, installed in a 

subsequent type or model aircraft. 

• Changes of display configuration (FMS/data link display), supporting system

(EICAS/ECAM) or other aircraft interface (DFDR, etc.). 

 (12) Initial TC/STC (as related to data link communications). The first FAA data link 

communications airworthiness approval (in accordance with a TC or STC) of any one or 

combination of the following components: a data link processor and/or management unit, data 

link communications avionics. 

NOTE: Previously approved data link communications systems, may 

require an initial TC/STC, if the part number of any of the above 

components changes due to a significant modification that changes, 

the system. 

 (13) Maintenance Review Board (MRB). An FAA board responsible for establishing 

maintenance requirements for a specific aircraft type. MRB requirements are usually formulated 

in conjunction with information provided by the manufacturer and prospective operators through 

industry working groups. FAA CHDOs apply MRB requirements in reviewing and approving 

each carrier's proposed maintenance program. 

 (14) Master Minimum Equipment List (MMEL). An FAA document listing 

stipulations in accordance with 14 CFR §§ 121.628 and 135.179 that provides authorization for 

the continuation of flight beyond a terminal point with certain equipment inoperative. AEGs 

develop MMELs in conjunction with a Flight Operation Evaluation Board (FOEB) established 

for each aircraft type. The MMEL, which is associated with a particular type of aircraft, serves 

as the basis for MELs, which are associated with an air carrier’s operation of that aircraft type. 

 (15) National Airspace System (NAS). Information on the NAS related to operations 

and use of air traffic data link services can be found in Aeronautical Information Publication, 

Airmen’s Information Manual, Notice to Airmen, Jeppesen Charts, or similar resources. The 

common network of U.S. airspace is comprised of the following: 

• Air navigation facilities 

• Equipment and services 

• Airports 

• Aeronautical charts 

• Rules 

Page 6 Par 7 
12/29/05 AC 120-70A 

• Regulations 

• Procedures 

• Technical information 

• Manpower 

• Materials 

• System components shared jointly with the military 

 (16) National Simulator Evaluation Team (NSET). Team of FAA operations 

specialists responsible for evaluating flight simulators to aid Principal Operations Inspectors 

(POI) in approving those simulators in accordance with regulatory requirements (e.g., NSET 

evaluations support POI approval of a particular simulator for use in a specific part 121 

program). 

 (17) Principal Inspector (PI). Refers to one of three FAA principal inspectors: 

principal avionics inspector (PAI), principal operations inspector (POI), or principal 

maintenance inspector (PMI). 

• Principal Avionics Inspector (PAI). The FAA inspector assigned responsibility 

for overseeing all avionics issues relative to a specific operator, including input to 

training programs, Operations Specifications, MEL requests, etc. 

• Principal Operations Inspector (POI). The FAA inspector assigned responsibility 

for overseeing all operational issues relative to a specific operator, including 

approval of training programs, Operations Specifications approval, maintenance 

programs, MEL change requests, etc. 

• Principal Maintenance Inspector (PMI). The FAA inspector assigned 

responsibility for overseeing all maintenance issues relative to a specific operator, 

including input to training programs approved maintenance programs, Operations 

Specifications, MEL requests, etc. 

 (18) Supplemental Type Certificate (STC). An FAA certificate certifying that 

modifications to the respective aircraft, engines, or other components meet airworthiness 

requirements of the regulations. 

 (19) Type Certificate (TC). An FAA certificate certifying that the respective aircraft, 

engines, or other components meet airworthiness requirements of the regulations. 

7. AUTHORIZATION TO USE DATA LINK COMMUNICATIONS IN FLIGHT 

OPERATIONS. 

Par 6 Page 7 
AC 120-70A 

a. General. 

 (1) Installation of a data link communication system requires FAA design approval of 

changes to the aircraft's type design by amending the TC or issuing an STC. However, approval 

to install a TC’d or STC’d data link communications system does not constitute approval to use 

the system. Prior to using the system, the operator must request a revision to their Operations 

Specifications to ensure that the system is used in accordance with international standards and 

requirements and in a manner that is acceptable to the FAA. A revision to the Operations 

Specifications includes specific authorizations, training and maintenance programs, manuals, 

operational procedures, MELs, and other such areas necessary for safe and effective use of data 

link communications. In addition, the service must be capable of meeting international standards 

for a specific route. 

 (2) Responsibilities of various FAA offices regarding data link communications. FAA 

ACOs approve changes to a type design or issuance of STCs. FAA AEGs formulate operational 

criteria for specific aircraft types related to training, checking, maintenance, MMELs or other 

operational issues, as necessary. FAA uses information developed by AEGs to review a 

particular operator's programs. CHDOs approve particular Operations Specifications, letters of 

authorizations, operator's training, maintenance programs, operational procedures, and MELs, if 

they are consistent with criteria specified in this Advisory Circular, Aeronautical Information 

Manual (AIM), MMELs, FSB reports, MRB reports, and policy guidance from Flight Standards 

Service AFS-200, AFS-300, AFS-400 and AFS-800. 

b. Design Approval of Aircraft Data Communications Systems. Guidelines of design 

approval of aircraft data communication and SATCOM voice systems and applications primarily 

used for ATS are provided in FAA AC 20-140 or equivalent. 

c. Operational Authorization. Criteria for data link operational authorization are 

determined by the communication requirements specified for the intended operation. 

 (1) Data link Communications Authorization Criteria. Operational authorizations 

are based on criteria in this AC, and may also include criteria outlined in, training, maintenance, 

MMEL, or other operationally related criteria formulated by AEGs. If criteria for training or 

checking are other than as specified in this AC, the criteria may be found in FSB reports 

applicable to a particular aircraft type. Provisions for dispatch with inoperative equipment are 

specified by the MMEL for each aircraft type. Maintenance requirements are identified by this 

AC, unless otherwise described by a MRB report for a specific aircraft type, or in FAA-approved 

maintenance instructions identified in conjunction with an STC or manufacturer's Service 

Bulletin.

(2) Data Link Communications Authorization Methods. FAA Flight Standards 

provides operational approval of data link communications training programs, checklists, 

operations manuals, training manuals, maintenance programs, MELs, and other pertinent 

documents or document revisions applicable to the particular air carrier. Operators' data link 

communications programs are usually approved for each specific aircraft type. However, 

Page 8 Par 7 
12/29/05 AC 120-70A 

programs common to one or more types may be approved if data link communications program

elements are common to different aircraft types. 

(3) Data Link Communications Authorization Procedures. 

 (a) Operational authorization to use data link communications is provided by an 

FAA POI. Operators should make early contact with their respective PI’s to permit timely FAA 

response. Usually such contact is initiated at the time preparations are being made for data link 

communications system selection or purchase. 

NOTE: Each operator is assigned three FAA PI’s; A POI, a PMI, 

and a PAI, that are typically located in the CHDO. 

 (b) Installations, training, maintenance programs, MELs, and other data link 

communications program elements are reviewed and approved by the FAA.

 (c) Prior to issuance of Operations Specifications, or the addition of an area, route 

or procedure to an existing Operations Specification, the operator should demonstrate that the 

aircraft data link system is compatible with that of the systems being used by the ATC facility 

when communicating with the chosen service provider(s). The results of prior interoperability 

demonstrations performed, as part of a design approval may suffice. Under international 

standards, the service provider(s) and air/ground data link communications sub-networks used in 

the performance demonstrations for design approval must be operationally equivalent to those in 

the proposed operating approval. Operational equivalence is determined by an assessment of the 

SPR and INTEROP standards, which may be demonstrated in an operational flight check. 

 (d) Following, determination of aircraft eligibility to use data link services, the 

operator should conduct an interoperability test to demonstrate that the specific combination of 

data link communication systems elements perform as intended (e.g., FMS ACARS interface, 

printers, CSP and air traffic facilities along the intended routes of flight). The PAI will review 

the test results for conformance with international standards and FAA policy and procedures. 

8. PART 121 FLIGHTCREW QUALIFICATION FOR USE OF DATA LINK 

COMMUNICATIONS. 

 a. General. 

 (1) Data link Communications Qualification Issues and Objectives. Separate 

qualification issues and training should be addressed depending on the system being used by the 

Par 7 Page 9 
AC 120-70A 12/29/05 

air carrier, (digital or analog data link). Air carriers should address the following issues and 

objectives to ensure appropriate flightcrew data link communications qualification: 

 (a) Provide necessary flightcrew knowledge of data link communications concepts, 

systems, and procedures (Data link Communications Academic Training). 

 (b) Develop necessary flightcrew knowledge and skills to properly respond to data 

link communications clearances or advisories (Data link Communications Procedure Training). 

 (c) Assess each pilot's ability to properly use data link communications (Data link 

Communications Initial Evaluation).

 (d) Identify Human Factors issues specific to flightcrew operation and interaction 

with the communication software, hardware, and operating environment (e.g., head-down time, 

situational awareness, and loss of party-line information). 

 (e) Maintain appropriate data link communications knowledge and skills which 

may include Data link Communications Recurrent Training. 

 (2) Data Link Communications Training. Flightcrew member training for first time 

use of data link services should be included in initial, transition, upgrade, recurrent, differences, 

or stand-alone qualification programs. Data link communications training could be included in 

specific aircraft qualification programs during transition, upgrade, or differences training (e.g., 

during DC-10 to B747-400 transition) or operators could conduct data link communications 

training in conjunction with general training (e.g., during initial “new hire” indoctrination, 

recurrent proficiency checks or proficiency tests, or line-oriented flight training. Data link 

communication training programs may also be developed as separate training programs (e.g., by 

completion of a standardized curriculum covering the general use of data link services at an 

operator’s training center or at designated crew bases). 

(3) Credit for Use of Other Programs. Operators may receive credit for existing data 

link communications training programs that are already approved in a different application. For 

example, an operator may receive credit for programs based on previous use of data link 

services, such as on different routes or for a different type of operation, or training programs 

conducted by another operator, training center, or manufacturer. The POI will determine 

whether and how much credit an operator should receive, considering whether the training 

program is used in another FAA approved application and whether the operator has 

demonstrated that the training program is relevant to the new application. AFS-400, NSET, or 

the assigned AEG may assist the POI in determining the suitability of a proposed data link 

training program for a particular operator’s procedures and aircraft capability. 

b. Data Link Communications Academic Training. The following subjects should be 

addressed in an approved program of data link communications academic training during the 

initial introduction of a crewmember to data link communication systems. For subsequent 

programs, only the new, revised, or emphasized items need be addressed.

Page 10 Par 8 
 AC 120-70A 

(1) General Concepts of Data Link Communications Operation. Academic training 

should cover, in general terms, data link communications systems theory to the extent 

appropriate to ensure proper operational use. Flightcrews should understand basic concepts of 

operations involving data link services, nominal and unacceptable performance, normal and nonnormal use, and limitations. 

 (2) Level of Capability Provided by Data link Communications and Expected 

Flightcrew Response. Academic training should explain the normal, expected pilot response to 

data link messages including acknowledgment, acceptance, rejection, or cancellation of a data 

link message. 

 (3) Data Link Communications Language, Terms and System Information. 

Flightcrews should be familiar with data link message sets, abbreviations and conventions used, 

contractions, terms, message addressing, facility and capability depiction on charts or in 

manuals, and terminology associated with applications (e.g., CPDLC, FIS, TWDL, ADS, ADS 

reporting contracts). 

 (4) ATS Communication, Coordination and Credits for Use of Data Link 

Communications. Crews should be advised of proper flight plan classifications to use and any 

ATS separation criteria, procedures, or MEL credits that are based on data link communications 

use. Training should include procedures for transitioning to voice communication and other 

contingency procedures related to the operation in the event of abnormal behavior of the data 

link services. This would include any necessary coordination with ATC related to or following a 

data link exceptional event and ensuring an acceptable transition to a new type of operation, such 

as procedures related to the transition to a different separation standard when data link services 

fail. 

 (5) Data link Communications Equipment Components, Controls, Displays, Audio 

Alerts, and Annunciations. Procedural training should include discussion of terminology, 

symbology, operation, and optional controls and display features, including any items particular 

to an air carrier’s implementation or the uniqueness of its aircraft capability and/or procedures. 

Applicable message sets, expected transmission times, failure annunciations, constraints, and 

limitations should be addressed. 

 (6) Interfaces and Compatibility with other Aircraft Systems. Training should 

include the management of any applicable data link air/ground communications systems and 

applications, including; VHF data link, SATCOM data link, HF data link, and Mode S. This 

training should also address voice integration with other cockpit systems, FMS inputs to data 

link, and electronic flight instrument system interfaces, including any items particular to an air 

carrier's implementation or uniqueness of its system. 

 (7) Aircraft Flight Manual (AFM) Information. AFM provisions should be 

addressed including information on data link communications modes of operation, normal and 

non-normal flightcrew operating procedures, response to failure annunciations, and any AFM 

limitations. 

Par 8 Page 11 
 AC 120-70A 

 (8) MEL Operating Provisions. Flightcrews, dispatch, and maintenance personnel 

should be familiar with the MEL requirements. 

 (9) Flightcrew Response. Appropriate pilot response to data link, SATCOM voice and 

other such issues. 

 (10) Data Link Event Reports. The air carrier's data link non-normal event reporting 

policies for flightcrews. 

 (11) Data Link Malfunction or Irregularity Reports. Data link malfunction or system

irregularity reporting procedures as used by aircrews, if not otherwise addressed by routine 

maintenance procedures of that operator. 

 (12) Human Factors. Flightcrew Human Factors are issues specific to the operating 

environment and operation of the installed communication system. 

C. Data Link Communications Operational Use Training. In addition to the academic 

training described in paragraph 8b, appropriate operational use training (e.g., to ensure use of 

proper procedures and response to data link advisories) should also be given. Data link use 

training should expose the pilot to the typical messages expected. 

 (1) Use training should include the following: 

• Receiving and interpreting messages 

• Accepting, rejecting or canceling messages 

• Storing and retrieving messages 

• Loading messages into appropriate controls/displays for use (e.g., FMS, FGCS) 

Formulating and sending messages 

• Loading message requests from the FMS (e.g., Flight plan WP’s into data link for 

transmission if applicable) 

• Managing the communications systems 

• Establishing and terminating system operation 

• Switching use of RF media (if this is a crew-controllable feature) 

• Re-establishing system operation after loss of network log-on 

 (2) In addition, training programs should cover the proper use of data link 

communication controls, procedures, and limitations. Correct assessment of displays, aural 

advisories, annunciations, timely and correct responses to data link communication failures and 

Page 12 Par 8 
12/29/05 AC 120-70A 

appropriate interaction with ATC following data link messages that are not acceptable. 

Recognition of data link communications system failures and data link issues unique to that air 

carrier should be taught. Such training may be conducted using data link communicationequipped flight training devices or simulators, or by using suitable CBI. Criteria for programs 

intending to address proper data link communications use through the use of simulators or 

training devices are listed in paragraph 8c(1). Criteria for programs intending to address proper 

data link communications use through CBI, and not using approved simulators or training

devices, are listed in paragraph 8c(2). Operators may apply provisions of either paragraph 8c(1) 

or 8c(2), or combinations of these provisions to address necessary initial and recurrent data link 

communications use training, as approved by the FAA for that operator's specific data link 

communication systems, training devices, and simulators. 

 (3) Programs Addressing Data link Communications that use approved simulators or 

training device programs based on use of FAA-approved training devices or simulators should 

realistically depict relevant aspects of data link communication procedures, clearances, and pilot 

responses. This may be accomplished using one or more of a combination of training methods 

described in paragraph 8a. Any simulator or training device used should have the characteristics 

described in paragraph 8m. 

 (4) Programs Addressing Data link Communications Procedures Through Use of 

Computer-Based Instruction (CBI). Data link communications programs may be approved 

which do not require using approved simulators or training devices if the proposed program

meets certain criteria as described below. These programs are based on CBI adequately 

depicting data link communications procedures, clearances, desired pilot responses, and resulting 

crew interactions with aircraft flight management systems. Such programs should include the 

issues identified in 8c(1), and be consistent with the following criteria: 

• Accepted FAA and industry guidelines 

• There should be no significant adverse training experience related to the 

particular data link communications system(s) 

• Differences from or compatibility with other data link communications systems 

(digital versus analog), that use different presentation methods, language, 

abbreviations etc., should be considered in the design to ensure minimum adverse 

human factor difficulties 

• The program should realistically depict data link communications scenarios 

• The training subject should be made aware of the normal delivery delays to be 

expected 

• Scenarios should demonstrate correct indications for messages, display 

annunciations, aural alerts, and require proper pilot responses 

d. Training Center Approval. Training centers may conduct data link communication 

training for an operator if approved by the POI. The POI will consider the following factors: 

Par 8 Page 13 
AC 120-70A 12/29/05 

 (1) Provisions of paragraphs 8b and 8c are shown to be met, or 

 (2) Equivalence to a previously approved program can be established. In this instance, 

circumstances, assumptions, and conditions for the program's use should also be equivalent to 

those applicable to the previously approved program. 

e. Initial Evaluation of Data Link Communications Knowledge and Procedures. 

Individual crewmember data link communications knowledge and procedures should be 

evaluated prior to data link communications use. Acceptable means of initial assessment 

include: 

 (1) Evaluation by an authorized instructor or check airman using a simulator or training 

device capable of depicting data link communication exchanges. 

 (2) Evaluation by an authorized instructor or check airman during line operations, 

training flights, PC/PT events, operating experience (OE), route checks or line checks. 

 (3) Computer-based testing in which data link communication scenarios and advisories 

are depicted and records acceptable pilot performance. 

 (4) Other alternate methods acceptable to the Administrator. Alternate methods should 

demonstrate the equivalent effectiveness of methods (1) through (3). 

NOTE: Instructors should evaluate initial data link crewmember 

communications for certificate holders that are authorized to use data link 

systems in their operations. 

f. Data Link Communications Recurrent Training. Data link communications training 

should be integrated as other established training programs and conducted on a recurrent basis. 

Recurrent training for data link communications should incorporate the recommendations of 

paragraph 8c and address any significant issues identified by line operating experience, system

changes, procedural changes, or unique characteristics. 

g. Data Link Communications Recurrent Evaluation. Recurrent data link 

communications checking should be incorporated as necessary, as an element of routine 

proficiency training or proficiency check programs. 

h. Data Link Communications Currency (Recency of Experience). Unless otherwise 

required in an operational specification, once crews have completed initial data link 

communications training and as long as recurrent training is accomplished in accordance with 

paragraph 8f the certificate holder will not be obligated to develop additional currency 

requirements. 

Page 14 Par 8 
12/29/05 AC 120-70A 

i. Line Checks and Route Checks. When data link communications-equipped aircraft are 

used during line or route checks, check airmen should routinely incorporate proper data link 

communications use as a discussion item.

j. Line-Oriented Flight Training (LOFT). LOFT programs using simulators equipped 

with data link communications should be enhanced by interaction with data link 

communications. In addition, LOFT programs should consider proper crew use of data link 

along with other communication methods (SATCOM voice, VHF voice, HF voice, etc.). 

k. Crew Resource Management (CRM). CRM programs should address effective 

teamwork in responding to data link exchanges. 

l. Data link communications Academic Training Methods. Appropriate methods may 

be suited to each air carrier's program. No special methods related to academic training for data 

link communications are identified. Typically, a combination of ground instruction, manual 

information, flightcrew bulletins, and other such means as appropriate to address academic 

topics specified by paragraph 8b, Data link communications Academic Training. 

m. Characteristics of Simulated Data Link Communications Systems for Training (e.g., 

data link communications in simulators or training devices). Reference paragraph 8c. 

 (1) Acceptable Characteristics. Training devices and simulators should have certain 

characteristics to be effective. This is due to the interactive nature of data link communications, 

the variety of exchange scenarios possible, the immediate and standardized pilot response 

required, and the correct display interpretation that is necessary. Thus, simulators or training 

devices used for data link communications training should have the following characteristics: 

• The ability to functionally represent data link communication displays, controls, 

indications, and annunciations. 

• Ability to depict selected message traffic exchange scenarios including data link 

communications displays and audio advisories. 

• Ability to show proper data link communications reaction to depicted scenarios 

and advisories, crew or ATC response errors, etc. 

• Ability to interactively respond to pilot inputs regarding data link communication 

advisories, including responses to failures or abnormal situations. 

(2) Simulator and Data Link Communications System Fidelity. For a particular data 

link communication system, training may be accomplished in simulators or training devices that 

represent the specific aircraft, or an aircraft with similar characteristics. For the purposes of data 

link communications training, simulators or training devices may use simplified algorithms or 

abbreviated message set capability. Data link communication displays do not have to be 

identical, but should be functionally equivalent to the air carrier operator's specific aircraft in 

use. 

Par 8 Page 15 
AC 120-70A 12/29/05 

(3) Training Device or Simulator Approval. Training devices or simulators meeting 

FAA criteria are qualified by the NSET and approved for use by the POI. Any one or 

combination of the following devices or simulators that meet characteristics of paragraph 8m (1) 

above, Acceptable Characteristics, may be used: 

• Level A through D simulators, 

• Level 4 through 7 flight training devices, or 

• Dedicated data link communications training devices acceptable to the FAA 

(including those devices described in FAA Order 8400.10, Air 

Transportation Operations Inspector's Handbook, volume 3, paragraph 443, 

"Aircraft Systems Integration Training" which are shown to be suitable for 

data link communications training). 

NOTE: Training device and simulator levels are defined by AC 120-40B, 

Airplane Simulator Qualification; AC 120-54 Advanced Qualification 

Program; and FAA Order 8400.10. 

9. OTHER OPERATIONAL ISSUES. 

a. Manuals and Other Publications. Airplane flight, operating, maintenance, general 

policy, or other manuals, publications, or written materials (e.g., operating bulletins) that may 

relate to data link communications use must be appropriately amended to describe data link 

communications equipment, procedures, and operational policies according to the appropriate 

guidance material in this AC. 

 b. MMEL/MEL. Operators formulate necessary data link communications revisions to 

their MEL(s) for each particular fleet (e.g., B727, DC10). The Federal Aviation Regulations 

require MEL revisions to be consistent with the FAA’s MMEL established for each aircraft type. 

A summary of the process for addressing the necessary changes to MEL items as well as 

examples of MMEL and acceptable MEL provisions for data link communications are provided 

in Appendix 2. 

c. Aircraft with Data Link Communications System Differences. Operators having 

aircraft with data link communication systems differences in displays, controls, or procedures, or 

operators involved with interchange operations, must account for those data link 

communications systems differences. This is accomplished as part of an approved differences 

training program in accordance with part 121, or as otherwise specified in applicable FAA FSB 

reports concerning crew qualification pertaining to a particular airplane type. 

d. Issues Unique to a Particular Operator. Operators should address any data link 

communications issues that may be unique to their particular route environment, aircraft, 

procedures, or data link communication displays and control features. Examples include the 

following: 

Page 16 Par 9 
12/29/05 AC 120-70A 

 (1) Examples of "Route Environment" Issues. Operators should describe any 

peculiarities associated with a particular route that may involve either end-user application issues 

or communications performance issues, for example: 

• On North Atlantic routes, it is necessary for data link oceanic clearance message 

verification to include the track message serial number in the response. 

• A particular route may be subject to propagation disturbances (e.g., with HF 

radio or HF Data Link at particular locations, time of day, season, or sunspot 

cycles). 

(2) Example of a "Procedural" Issue. Operators should describe any data link 

precautions that may be appropriate when operating in states where data link communications 

policies are uncertain. As an example, certain modes of direct controller-pilot data link 

communication may not be supported in certain states. In those cases, carriers should conform

to the laws and regulations that govern the airspace being used and use only authorized 

communications equipment and methods. This guidance should be reflected in company flight 

operations manuals. 

(3) Example of a "Unique Data Link Communications System" Issue. Operators 

should describe any differences in particular data link communications systems, or their 

versions, that may have operational impact. For example, Boeing FMS “Load 11” software 

requires a workaround solution for incorporating the aircraft tail number in data link messages, 

whereas “Load 12” does not. 

10. MAINTENANCE. 

 a. General. Maintenance procedures for data link communications are approved or 

accepted as part of an operator's initial maintenance manual approval or as a revision to that 

manual. To obtain FAA authorization, an operator must demonstrate that their data link 

communications maintenance procedures are consistent with the data link communications 

systems manufacturer's maintenance procedures and/or aircraft manufacturer's maintenance 

procedures for data link communications. 

 b. Maintenance Training. Operators should provide adequate data link communication 

maintenance training to ensure that their maintenance personnel or contract maintenance 

personnel at facilities not staffed by the operator, are able to properly implement data link 

communications-related maintenance programs. This includes, but is not limited to, installation, 

modification, correction of reported system discrepancies, use of test equipment, procedures, 

MEL relief, and "return-to-service" authorizations. The training procedures should address 

testing data link communications on the ground in such a way that correctly evaluates data link 

communications functions while not introducing hazards with respect to simulated message 

traffic with an air traffic facility. 

c. Data Link Communications System Software Updates. Operators should assure that 

appropriate data link communication software updates are incorporated when necessary and that 

Par 9 Page 17 
AC 120-70A 12/29/05 

both air and ground system are able to identify and properly respond to the installed level of data 

link communication capability. 

d. Data Link Communications "Return to Service" Policies. Data link communications 

"return to service" policies should be established to ensure proper data link communications 

functions when an aircraft is returned to service after a datalink communication failure or 

maintenance action. 

11. DATA LINK COMMUNICATIONS OPERATIONAL USE.

 a. General. Operationally, those skills addressed and the guidance provided in the data link 

communications training paragraph 8 should be followed and implemented by each operator 

electing to use data link communications. 

 b. Pilot Responsibilities. Data link communications are intended to serve as either a 

primary or supplementary communications means as designated for the operations being 

conducted. For data link communications to work as designed, prompt and correct initiation 

response to data link advisories is important. Flightcrews using data link communications 

should respond in accordance with the following guidelines: 

 (1) Prompt initiation of messages where needed. 

 

 (2) Prompt response to messages where appropriate. 

 (3) Appropriate crew coordination so that each crewmember receives pertinent 

information needed. 

 (4) Appropriate retention of messages (archive) requiring later action (printer copies of 

oceanic clearances etc.). 

 (5) Appropriate resolution of message uncertainty.

 (6) Appropriate use of data link and voice, respectively, where circumstances or 

operations dictate (e.g., voice for backup or clarification of non-normal situations). 

 (7) If an ATC data link clearance contradicts a voice clearance, comply with the voice 

clearance. 

c. Data Link Communications Good Operating Practices. The following data link 

communications "good operating practices" have been identified: 

 (1) To preclude unnecessary communication and possible interference with ground 

facilities, data link communications should be used only in conjunction with facilities specified 

for the route or procedure to be flown. An example would be as follows: data link 

communications with other than designated ground facilities should be accomplished only as 

necessary to support flight plan or flight operations requirements. 

Page 18 Par 11 
12/29/05 AC 120-70A 

 (2) Free text data link messages should use standard aeronautical terminology, accepted 

abbreviations, and be written in English. 

 (3) When appropriate, verify data link communication functions prior to departure. 

d. Operator Responsibilities. Operators have the following general responsibilities 

regarding data link communications: 

 (1) Verify data link communications functionality for each environment to be used and 

when new or modified components or software are introduced. 

 (2) Assure follow-up and evaluation of exceptional data link events. 

 (3) Periodically assess data link communications training, checking, and maintenance 

programs to ensure their correctness, pertinence, timeliness, and effectiveness. 

 e. ATC Responsibilities. The operator can expect ATC to adhere to the following 

procedures. 

 (1) Ensure that controllers do not knowingly issue data link instructions that are contrary 

to voice instructions when a data link is being used. 

 (2) Be aware of pertinent data link communication program changes. 

 (3) Train ATC specialists about data link expected flightcrew responses to data link 

advisories, and permit familiarization flights for specialists on data link equipped aircraft to the 

extent possible. 

 (4) When requested by the flightcrew, provide clarification or confirmation of data link 

messages and assist in returning to the assigned clearance, if appropriate. Issue additional 

clearance instructions when the situation so requires. 

 (5) Advise pertinent FAA offices via data link communications questionnaires about 

airspace or airports where data link communications problems occur. This facilitates initiation 

of corrective actions related to data link communications enhancements, procedures, and 

airspace adjustments. 

 (6) Advise FAA if aware of other hazardous conditions, situations, or events which may 

be related to data link communications. 

12. DATA LINK EVENT REPORTING.

 a. General. Operators and manufacturers are encouraged to develop procedures to ensure 

effective identification, tracking, and follow up of data link-related events, as appropriate. Such 

procedures should focus on providing useful information to: 

Par 11 Page 19 
AC 120-70A 12/29/05 

 (1) Properly assess the importance of data link events, 

 (2) Follow up on information related to specific data link events as necessary. 

 (3) Keep the industry and FAA informed on the performance of data link in the NAS 

and international operations. 

 b. Pilot Reports. 

(1) "Data Link-Specific" Reports. Pilots should make the following reports for 

unusual data link events, as necessary: 

 (a) Upon query from ATC, or after an inadvertent deviation from an ATC 

clearance, make radio communications as appropriate to report the event. Refer to the 

Airman's: Information Manual, Section 4, ATC Clearances, for guidance regarding 

recommended phraseology, and Appendix 5 of this AC for acronyms and abbreviations. 

 (b) Reports, as specified by the operator, concerning data link anomalies, 

procedural difficulties, or system failures typically are made by pilots through one or more 

of the following methods 

• Pilot/Observer Questionnaire, 

• Logbook entry, ACARS, etc., or 

• Other record used by that operator (e.g., "Captain's Report"). An example of a 

typical reporting form for data link event information is shown in 

Appendix 1. 

 (2) Other Reports Incidental to Data Link. 

 (a) Near Mid-Air Collision, NMAC Reports. Flightcrews should continue to 

submit NMAC reports in accordance with existing policies and procedures. (Crews should be 

aware that there is no requirement to submit an NMAC report solely due to a data link event). 

 (b) Aviation Safety Reporting System (ASRS) Reports. ASRS reports may be 

filed at the discretion of the flightcrew. 

 (c) Operator/Maintenance Department Reports. Operator maintenance 

department personnel should make data link-related reports as necessary. Submit reports of 

frequent or systematic data link problems that may relate to system performance, manufacturers, 

and/or data link vendors to the PAI or PMI, as appropriate. 

 (d) FAA ATC. Report the following: 

• Data link events to FSDOs as necessary 

Page 20 Par 12 
12/29/05 AC 120-70A 

• Any exceptional data link-related events regarding NAS performance to 

the Air Traffic Procedures Division 

 (e) Data Link Manufacturer Reports. Data link avionics manufacturers report 

problems found with specific data link systems in accordance with established service difficulty 

report (SDR) procedures. Generic problems, such as those that may relate to the definition of 

ARINC 622 or 745 characteristics or of documents listed in paragraph 4(c) should be reported to 

the Aircraft Engineering Division, AIR-200 (Production/Airworthiness). 

13. FOREIGN AIR CARRIERS. 

a. General. Foreign air carriers may use data link communications when operating in U.S. 

airspace. Foreign air carriers are not required to install and use data link communications for 

any aircraft or operations even though separation services may be provided by a U.S. ATC 

facility 

(e.g., in oceanic airspace), unless separation standards or a desired flight plan classification are 

based on its use. 

b. Data Link Communications Approval for Foreign Air Carriers. FAA does not 

approve data link communications installations, training programs, MELs, or maintenance 

programs for foreign operators operating non-U.S. registered aircraft. Such authorizations are 

addressed as specified by the state of the operator. However, since compatibility of data link 

communications within U.S. airspace is essential, part 129 operations guidelines for data link 

communications are issued by this AC. Compliance with these data link communications 

provisions ensures both data link communication system and procedural compatibility. The 

issuance of operations specifications (OpSpecs) or an amendment to existing OpSpecs for data 

link communications must take place prior to a foreign air carrier operating a data link 

communication-equipped aircraft in Domestic U.S. airspace, or with U.S. Domestic facilities. 

Standard provisions for foreign air carriers for data link communications are shown in 

Appendix 3. 

c. Application and Approval. Foreign air carriers should contact their FAA POI to obtain 

application information for part 129 data link communications OpSpecs in U.S. airspace. When 

a foreign air carrier submits the necessary information to the respective PI, showing that its 

aircraft comply, the PI approves those OpSpecs or an amendment. Standard OpSpec provisions 

regarding data link communications for foreign air carriers are shown in Appendix 3. Although 

not mandatory, foreign operators should comply with the provisions of this AC, or equivalent 

provisions specified by the state of the operator or specified by ICAO. 

Par 13 Page 21 

12/29/05 AC 120-70A 

 Appendix 1 

APPENDIX 1. 

SAMPLE DATA LINK EVENT REPORTING INFORMATION 

Date____________________ Time__________________

Operator/Flight #_________ Origination_____________ Destination_____________

Submitted to: ATC Inquiry___________ Other_________________ 

Phase of Flight___________ Position__________________ Altitude_____________ 

(Optional for Aircrew:) 

Name_____________ Phone (W)_______________ Phone (H)_____________ 

Describe Event: 

Page 1 (and 2)

12/29/05 AC 120-70A 

 Appendix 2 

APPENDIX 2. 

DATA LINK COMMUNICATIONS MINIMUM EQUIPMENT LIST (MEL) 

AND MASTER MINIMUM EQUIPMENT LIST (MMEL) PROVISIONS 

1. EXAMPLE OF A MINIMUM EQUIPMENT LIST (MEL). Each operator intending to 

have authority to dispatch an aircraft with a data link communication system or component 

temporarily inoperative must do so in accordance with provisions of an MEL. MEL’s are 

approved for each operator and type aircraft, within provisions of the FAA MMEL for that type. 

When proposed, MEL provisions are consistent with the FAA MMEL; POI’s may approve the 

MEL. If less restrictive MEL or different MEL provisions are requested, a proposal for 

consideration of an FAA MMEL change must be forwarded to the AEG assigned for that aircraft 

type. Enhanced features (those above and beyond the basic data link communication system) 

may be inoperative, provided that the inoperative features do not degrade the system; for 

example, data link printers. 

Equipment Condition

Data Link system C-0 *(M) May be inoperative provided the system is deactivated and 

secured. 

Dual data link or 

data link controls or 

displays 

C-21 *(0) May be inoperative on the flying pilot side provided that: 

(a) Appropriate data link elements and functions are operative 

on the non-flying pilot side, and 

(b) Display data link indications are visible to the flying pilot. 

(0) May be in-operative on the non-flying pilot side, provided 

that: 

(a) The required minimum voice communications are operative 

and that voice procedures are approved for the route or 

procedures to be flown, and 

(b) The required minimum voice command communications 

audio functions are operative, and voice procedures may be 

used for the route or procedures to be flown. 

Data Link Printer C-0 (0) May be inoperative provided all other data link display and 

control functions are operative. All elements of each data link 

transmission can be retrieved, displayed and reviewed by the 

flightcrew or may be inoperative if relevant operations or 

functions are not predicated on data link use (e.g., Print Control 

function not authorized if the printer is inoperative). 

Page 1 
AC 120-70A 12/29/05 

Appendix 2 

2. EXAMPLE OF A DATA LINK MASTER MINIMUM EQUIPMENT LIST (MMEL) 

PROVISION. 

Boeing 747-400

23 COMMUNICATIONS | | | | | 

| | | | | 

 -XX-1 Digital Data Link |D | - | - | Any in excess of those required by | 

 Communications Systems | | | | Regulation may be inoperative. | 

| | | | | 

 -XX-2 Analog Data Link |D | - | - | Any in excess of those required by | 

 Communications Systems Regulation may be inoperative. | 

NOTE: The provisos and repair category intervals are intended to grant the 

operator sufficient relief during the initial stages of the data link 

implementation. This is intended to promote the installation process, as well as 

support the use of a partial system. Both equipment reliability and operational 

experience will dictate, if any, revision to this MMEL relief should be considered 

after the installation phase is completed. 

Page 2 
12/29/05 AC 120-70A 

 Appendix 3 

APPENDIX 3. 

PART 129 PROVISIONS FOR USE OF DATA LINK IN U.S. AIRSPACE

1. The issuance of operations specifications (OpSpecs) or an amendment to existing OpSpecs 

for data link communications must take place prior to a foreign air carrier operating a data link 

communication-equipped aircraft in Domestic U.S. airspace, or with U.S. Domestic facilities. 

2. An appropriate data link must be installed and operated on suitable frequencies specified by 

ATC during flight in U.S. airspace if procedures are predicated on its use. A unique and specific 

address, the ICAO 24-bit aircraft identification, must be assigned to the airplane and the data 

link must recognize this address. When properly set, the unique address, may not be altered, set 

to a duplicated address, or set to an address that potentially interferes with ATC or data link 

safety functions. 

3. A data link capable of coordinating with air traffic facilities using RTCA DO-219 or other 

equivalent standards must be installed if operations will be predicated on its use. The data link 

system should be operated in an appropriate data link mode during flight in U.S. airspace using

data link, except as provided for by MEL provisions acceptable to the State of the operator. 

4. Training and procedures for use of data link as specified by ICAO, this AC, or other 

equivalent criteria acceptable to the FAA, should be used when operating in U.S. airspace. 

5. Unsafe performance or conditions related to data link operations which potentially could 

affect continued safe operations in U.S. Airspace, (a data link event), should be reported to the 

FAA within 10 days of the time that such a hazard is identified. 

Page 1 (and 2) 

12/29/05 AC 120-70A 

 Appendix 4 

APPENDIX 4. 

ACRONYMS AND ABBREVIATIONS 

AAR Office of Aviation Research 

AC Advisory Circular 

ACARS Aircraft Reporting and Communications System

ACO Aircraft Certification Office 

ADS Automatic Dependent Surveillance 

AEG Aircraft Evaluation Group 

AFM Airplane Flight Manual 

AFS Flight Standards Service (FAA) 

AGL Above Ground Level 

AIR Aircraft Certification Service (FAA) 

AMSS Aeronautical Mobile Satellite Service (sometimes (AMS(R)S specifically for safety 

services) 

AOC Aeronautical Operational Control 

ASRS Aviation Safety Reporting System

ATC Air Traffic Control 

ATCRBS ATC Radar Beacon System

ATIS Automated Terminal Information Service 

ATP Air Traffic Procedures Division (FAA) 

ATS Air Traffic Service 

ATM Air Traffic Management 

ATN Aeronautical Telecommunication Network 

CAA Civil Aviation Authority 

CBI Computer-Based Instruction 

CHDO Certificate-Holding District Office 

CNS Communications/Navigation/Surveillance 

CFR Codified Federal Regulations 

CPDLC Controller-Pilot Data Link Communication 

D-ATIS Digital Automated Terminal Information System

DC Data Link communications 

DCPC Direct Controller-Pilot Communication (voice or data) 

DL Data Link 

EICAS Engine Indicating and Crew Alerting System

EFIS Electronic Flight Instrument System

FAA Federal Aviation Administration 

FANS Future Air Navigation System

FMS Flight Management System

FOEB Flight Operation Evaluation Board 

FSB Flight Standards Board 

FSDO Flight Standards District Office 

HF High Frequency (radio) 

ICAO International Civil Aviation Organization 

LOA Letter of Authorization

 Page 1 
AC 120-70A 12/29/05 

Appendix 4 

LOFT Line-Oriented Flight Training 

MASPS Minimum Aviation System Performance Standards 

MEL Minimum Equipment List 

MMEL Master Minimum Equipment List 

MRB Maintenance Review Board 

NAS National Airspace System

NAT North Atlantic 

NMAC Near Mid-Air Collision 

NSET National Simulator Evaluation Team

NTSB National Transportation Safety Board 

OE Operating Experience 

PAI Principal Avionics Inspector 

PC Proficiency Check 

PDC Pre-Departure Clearance 

PI Principal Inspector 

PMI Principal Maintenance Inspector 

POI Principal Operations Inspector 

PT Proficiency Training 

RCTP Required Communication Technical Performance 

SATCOM Satellite Communications 

STC Supplemental Type Certificate 

TC Type Certificate 

TSO Technical Standard Order 

VDL VHF Data Link 

VHF Very High Frequency (radio)

 

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