Ms. Margaret Gilligan October 24, 2013

Associate Administrator for Aviation Safety

Federal Aviation Administration

800 Independence Avenue

Washington, DC 20591

Mr. David Grizzle

Chief Operating Officer for Air Traffic Organization

Federal Aviation Administration

800 Independence Avenue

Washington, DC 20591

Dear Ms. Gilligan and Mr. Grizzle

The Unmanned Aircraft Systems Aviation Rulemaking Committee (UAS ARC) is pleased to 

submit the enclosed recommendations for inclusion of UAS language into 14 CFR § 91.113 (b)

for your consideration. This body of work represents the UAS ARC’s 91.113 Working Group

evaluation and review process. This team is made up of subject matter experts from within 

both the UAS community and the greater aviation community at large. 

The 91.113 Working Group assessed terminology currently published in 14 CFR as well as other 

FAA and ICAO publications for inclusions in this work. They also leveraged the UAS ARC’s 

Terminology and Classification Action Team’s (TCAT) recommendations. Whenever possible, 

they reviewed and updated existing terminology to better represent the current state of the 

UAS terminology nationally and internationally.

The UAS industry will benefit from the FAA’s formal recognition of the UAS ARC’s 91.113 

recommendations for UAS Detect and Avoid language. This recognition will facilitate the 

operational use of UAS in the NAS and be the cornerstone for regulatory work on Detect and 

Avoid.

The UAS ARC appreciates your continued support of its activities and invites you to discuss any 

aspects of these recommendations at your earliest convenience. The UAS ARC respectfully 

requests the FAA to provide us with a formal response. The members and constituents of UAS 

ARC will support FAA actions to develop and implement this recommendation.

Sincerely,

Robert Scott Dann

Chairman 

Unmanned Aircraft Systems

Aviation Rulemaking Committee
1

Unmanned Aircraft System (UAS) 

Aviation Rulemaking Committee (ARC)

Part 91 Working Group

Recommendations for 14 CFR 91.113 on 

Right of Way Rules for Unmanned Aircraft

August 2013
2

Table of Contents

1. Overview .................................................................................................................................................3

2. Background .............................................................................................................................................3

3. Discussion................................................................................................................................................4

4. Definitions...............................................................................................................................................6

5. References...............................................................................................................................................7

6. Acronyms.................................................................................................................................................7
3

1. Overview

The Federal Aviation Administration (FAA) currently requires a Certificate of Waiver or 

Authorization (COA) for public, civil, or commercial Unmanned Aircraft System (UAS) operations 

in the National Airspace System (NAS).

1

These special authorizations are required, at least in 

part because 14 CFR 91 rules were written for aircraft with a pilot in the cockpit onboard the 

aircraft. Specifically § 91.113 discusses right-of-way rules, and requires vigilance to be 

maintained by each person operating an aircraft so as to “see and avoid” other aircraft. The 

UAS ARC Part 91 Working Group recommends the addition of a sentence under Part 91 Subpart 

B—Flight Rules § 91.113 (b) that specifically addresses UAS. The recommended language is

(underlined language is new):

Part 91 Subpart B—Flight Rules § 91.113

(b) General. When weather conditions permit, regardless of whether an operation is 

conducted under instrument flight rules or visual flight rules, vigilance shall be maintained by 

each person operating an aircraft so as to see and avoid other aircraft, except as noted in 

paragraph (b)(1) of this section. When a rule of this section gives another aircraft the rightof-way, the pilot shall give way to that aircraft and may not pass over, under, or ahead of it 

unless well clear.

(1) For a UAS, vigilance shall be maintained so as to detect and avoid other aircraft.

2. Background

The guiding principles provided to the Part 91 WG by the UAS ARC steering group in 

development of this new language were to maintain the current level of safety in the NAS and 

to not impact the interpretation of the current language for manned aviation. The steering 

group acknowledged that some reference to a new exception may be required in § 91.113 (b), 

but directed that no other deletion, modification, or additional words to the existing § 91.113

(b) be made. Adding the reference to the end of the first sentence reduces any confusion that 

the exception in § 91.113 (b) (1) only applies to the first sentence, and the second sentence 

would apply to all aircraft including UAS. The intent of the new rule language is to enable an 

alternate means of compliance without requiring an exemption to the current rule. The

steering group also advised the WG that the new rule must apply to all classes of airspace, and 

that it should enable technology expansion without requiring future rule revisions. To focus the 

WG on this first phase, the steering group directed attention to the portion of the paragraph 

that states “vigilance shall be maintained by each person operating an aircraft so as to see and 

avoid other aircraft” in association with both avoiding collisions and remaining well clear. The 

WG will look to address other portions of § 91.113 and other Part 91 rules in the second phase.

All WG members agree to this approach; however, there is some difference of opinion on the 

specific words and definitions to be used. The WG attempted to keep the changes simple so as 

to minimize addition of new terms and definitions, but to ensure the language satisfies the 

guiding principles provided by the steering group. The WG recognizes this is a recommendation 
4

to the FAA and is not the final rule, so every attempt is made to capture in this paper the 

rationale for all options and alternatives.

3. Discussion

In the existing language of § 91.113 (b), the first part of the paragraph references “when 

weather conditions permit, regardless of whether an operation is conducted under instrument 

flight rules or visual flight rules.” All WG members agreed that the new § 91.113 (b) (1) specific 

to UAS would omit this language with the rationale that the individual UAS operations manual 

would specify under what weather conditions the UAS could operate. This position was 

reinforced by feedback from the steering group.

For the new sentence, a term is needed to identify the type of aircraft the new rule applies to. 

The two terms in prevailing use today are “Unmanned Aircraft System (UAS)” and “Remotely 

Piloted Aircraft System (RPAS).” There was about a 50/50 split within the WG on whether to 

use the terms UAS/UA or RPAS/RPA. The WG’s discussion of these terms and an option for 

avoiding both terms is summarized below. In addition, an alternative sentence in lieu of the 

recommended sentence is provided for each term.

a) The term “UA/UAS” is described in the FAA Modernization and Reform Act of 2012, 

which states, “The term ‘unmanned aircraft’ means an aircraft that is operated without 

the possibility of direct human intervention from within or on the aircraft. The term 

‘unmanned aircraft system’ means an unmanned aircraft and associated elements 

(including communication links and the components that control the unmanned aircraft) 

that are required for the pilot in command to operate safely and efficiently in the 

national airspace system.”

2 UAS is the more encompassing term that allows for various 

levels of automation. By using the term UAS in the language now, we allow for

technology expansion and preclude having to re-write the rule if autonomous aircraft 

are accepted at some point in the future. Every UA will be under some level of 

automation, which must be included in the UAS definition. As automation increases, 

the balance of flight operation duties shifts from the pilot to the UAS. The FAA UAS 

Concept of Operations Version 2.0 uses the term UAS, but also states the pilot in 

command will have full control or override authority to assume control at all times 

during normal operations and that routine autonomous operations are not permitted. 

In addition, the UAS ARC Terminology and Classification Action Team (TCAT)

recommended UAS as an over-arching term that includes both RPAS and autonomous 

aircraft. The recommended rule language would allow for future expansion of UAS 

automation. An alternative to the recommended rule language would be to add the 

following words: “by each person operating a UA.” This alternative would focus the rule 

on the requirement of the pilot to remain vigilant, but may limit future expansion. 

(1) For a UAS, vigilance shall be maintained by each person operating a UA so as to 

detect and avoid other aircraft.
5

b) The term “RPA/RPAS” is defined in the International Civil Aviation Organization (ICAO)

Annex 2. For “RPA” the definition is: “An unmanned aircraft which is piloted from a 

remote pilot station.”

3

The term “RPAS” is defined as: “A remotely piloted aircraft, its 

associated remote pilot station(s), the required command and control links and any 

other components as specified in the type design.”

3

These definitions make clear the 

involvement of a pilot. This involvement may include some supervisory role even if the 

aircraft performs some lower-level automation which the pilot only oversees. The ICAOdefined RPAS term is now widely accepted on a global basis. Focusing the rule change 

on RPAS, which always involves a pilot, may expedite the FAA’s rulemaking process.

Broadening the scope of the rule to UAS which includes autonomous aircraft may 

complicate the approval process. The UAS ARC Terminology and Classification Action 

Team (TCAT) in August 2012 recommended the ICAO Circular 328 term RPA to make 

clear the involvement of the pilot and harmonize with the international community. 

ICAO Circular 328 defined RPA as: “An aircraft where the flying pilot is not on board the 

aircraft. Note: This is a subcategory of unmanned aircraft.”4An alternative to the 

recommended rule language using the term RPA/RPAS would focus solely on the pilot in 

command and not allow for expansion to autonomous aircraft.

(1) For a RPAS, vigilance shall be maintained by each person operating a RPA so as to 

detect and avoid other aircraft.

c) To avoid the issue of using UAS or RPAS, the WG discussed an alternative to describe the 

intent. The intent of the WG is that the UAS, including when possible the UAS pilot,

must maintain vigilance so as to detect and avoid other aircraft.

(1) Aircraft without the pilot in command onboard shall maintain vigilance so as to 

detect and avoid other aircraft.

No matter which term is used, the loss of the command and control (C2) link will require an 

automated mode for safe UAS operation. The consensus of the WG was that a significant loss 

of the C2 link (definition and criteria to be determined in Phase 2) is considered an emergency 

condition and is covered under § 91.113 (c) “In distress. An aircraft in distress has the right-ofway over all other air traffic.” Subpart B of Part 91 is focused on the pilot’s responsibility and 

Subpart C of Part 91 is focused on the equipage. Therefore, the topic of lost C2 link must be 

addressed in another section of Part 91, if it is not already adequately addressed in § 91.113 (c). 

The other part of the paragraph that needs to be addressed is the word “see” in the phrase 

“see and avoid” in the existing § 91.113 (b). Several words, including “sense”, “detect”, and “be 

aware of” were considered as substitute for the word “see.” The WG members all agreed on 

the term “detect” as the best word to use. The rationale for this word choice is summarized 

below in Section 4.
6

4. Definitions

There is additional work in Phase 2 of this WG to include definitions of the terms introduced in 

this paper, but we wanted to include the discussions of the WG and the intent of the terms 

used. Though the WG agreed on the term “detect and avoid,” there was a split on how the 

term should be defined in the glossary (i.e., not included in § 91.113 (b)), which can then be 

referenced in § 91.113 (b) as well as other portions of 14 CFR Part 91. 

The recommended definition is “Detect and avoid is the capability to see, sense or detect 

other aircraft and take the appropriate action to remain well clear from and to avoid 

collisions with other aircraft.”

The WG agreed that “see and avoid” means more than collision avoidance, so the new term 

must work for other functions such as maintaining situational awareness and determining right

of way. The WG also agreed that the definition chosen should be harmonized with the terms 

used by RTCA SC-228, especially if avoiding other hazards is included in the definition. 

However, half the WG believes we should directly adopt the ICAO language and show alignment 

with the international community while the other half prefers to modify the ICAO language 

replacing the phrase “conflicting traffic or other hazards” with simply “other aircraft” and add 

specific actions.

The definition in ICAO Annex 2 is: “The capability to see, sense or detect conflicting traffic or 

other hazards and take the appropriate action.”

3

Based on the Sense and Avoid (SAA) for UAS Workshop report, the WG agreed on the intent of 

the definition for SAA. The definition is: “SAA is the capability of a UA to remain well clear from 

and avoid collisions with other airborne traffic. SAA is the combination of UAS Self-Separation 

plus Collision Avoidance as a means of compliance with 14CFR Part 91, §91.111 and §91.113.”5

This brings into discussion three topics to consider for the definition of “detect and avoid.” In 

the general glossary definition:

a) Does all traffic need to be detected, or just the conflicting traffic? The new proposed 

sentence in § 91.113 (b) (1) states “to detect and avoid other aircraft” where the last 

two words are a direct lift from the existing language in §91.113 (b). Therefore, the 

current language does not limit this function to only those aircraft in conflict. The WG’s

recommendation is to use the term “other aircraft.”

b) Should the UAS just avoid aircraft or other hazards (e.g., ground obstacles) as well? The 

current language in § 91.113 (b) does not specify the need to detect and avoid other 

hazards. The WG’s recommendation is to not include “other hazards” in the definition.

c) Do we leave open to interpretation what the appropriate action for the avoidance 

maneuver is, or should we further define the actions to be taken? The ICAO initially 
7

established ICAO Circular 328 in 2011 prior to the approval of the Annex 2 language that 

had the additional, “and take the appropriate action to comply with the applicable 

rules of flight.”

4

The WG’s recommendation is to specify avoidance actions in relation to 

remaining well clear and avoiding collisions recognizing the definition may have to be 

modified later if the term “detect and avoid” is to be used elsewhere in Part 91. This 

also aligns with the guidance provided by the steering group.

5. References 

1

FAA NOTICE N 8900.227, 30 Jul 2013.

2

FAA Modernization and Reform Act of 2012, 14 Feb 2012.

3

International Standards, Annex 2 to the Convention on International Civil Aviation, Tenth 

Edition July 2005 Amendment 43, 15 Nov 2012.

4

International Civil Aviation Organization Circular 328, Mar 2011.

5

Sense and Avoid (SAA) for Unmanned Aircraft Systems (UAS) Workshop report, 9 Oct 2009.

6. Acronyms

ARC Aviation Rulemaking Committee

COA Certificate of Waiver or Authorization

FAA Federal Aviation Administration

ICAO International Civil Aviation Organization

NAS National Airspace System

RPA Remotely Piloted Aircraft

RPAS Remotely Piloted Aircraft System

TCAT Terminology and Classification Action Team

UA Unmanned Aircraft

UAS Unmanned Aircraft System

WG Working Group