REPLY TO 

ATTENTION OF 

SFAE-AV 

DEPARTMENT OF THE ARMY 

PROGRAM EXECUTIVE OFFICE, AVIATION 

5667 WOOD ROAD 

REDSTONE ARSENAL AL 35898-5000 

2 9 SEP l\114 

MEMORANDUM FOR Federal Aviation Administration, Office of Rulemaking, Airmen 

and Airspace Rules Division (FAA, Keira Jones), 800 Independence Ave SW, 

Washington, DC 20591 

SUBJECT: Petition For Exemption From The Total Latency Provision of 14 CFR (Code 

of Federal Regulation) Part 91.227 For The U.S. Army Unmanned Aircraft 

1. This petition requests an exemption from a provision of 14 CFR Part 91.227 for the 

U.S. Army Unmanned aircraft fleet. This petition follows the requirements for inclusion 

in such documents set forth in the order presented in 14 CFR Part 11.81: 

a. The requested exemption is for 14 CFR 91.227 (e)(1). 

b. The extent of relief is from the allowed 2 seconds total latency increasing to 3 

seconds total latency. 

2. The U.S. Air Army requests an exemption from compliance with the 14 CFR 91.227 

(e)(1) because: 

a. Tests conducted on our HH-60L aircraft revealed that, with its current architecture 

and avionics, it would exceed the CFR's overall 2-second total latency requirement, but 

will be able to transmit the information within 3-seconds. Furthermore, comparing the 

results from the HH-60L and expanding it across the U.S. Army fleet of Unmanned 

Aerial Systems (UAS) which will be in service post January 2020, our assessment is 

that planned Automated Dependent Surveillance-Broadcast (ADS-B) Out modification 

efforts for many other aircraft may not achieve the 2-second limit, but would achieve a 

3-second latency. 

b. If the 2-second latency is not achieved with current architectures, the only way to 

meet the current 2-second requirement would be through aircraft modifications such as 

upgrading processors, adding wiring harnesses and/or modification of the bus 

architectures. Since the U.S. Army fleet of UAS are slow movers, under 200 knots, an 

FAA study of fast moving versus slow moving aircraft has shown there are no 

appreciable safety issues for slow movers who meet 3-second latency. 

c. Our Independent Government Cost Estimate (IGCE) to integrate ADS-B Out, 

which we have programmed funds for, would meet 3-second latency for our aircraft's 
SFAE-AV 

SUBJECT: Petition For Exemption From The Total Latency Provision of 14 CFR (Code 

of Federal Regulation) Part 91.227 For The U.S. Army Unmanned Aircraft 

current architecture and avionics. However, to meet the 2-second limit may involve 

extensive aircraft modifications, while not providing an appreciable safety benefit. 

3. Granting this request would be in the public interest and benefit the public as a 

whole: 

a. Save Taxpayer Money. A relaxation of the requirement from 2 to 3 seconds will 

meet the safety needs of the FAA, while saving integrations funds for the U.S. 

Government and American taxpayer. Per an FAA analysis for slow moving aircraft, the 

FAA agreed 3-second latency does not pose an appreciable safety issue, so the 

additional expense to meet 2-second latency is not justifiable. 

b. Lack of Funding. Army Aviation has programmed funding to integrate ADS-8 

Out into Army platform's current architecture and avionics. However, we have not 

programmed funding that would be required in upgrading processors, adding wiring 

harnesses and/or modification of the bus architectures in order to decrease the latency 

from 3-seconds to 2-seconds. With budgets under scrutiny and declining, obtaining 

additional funds to meet 2-second latency would be difficult. 

4. Granting the exemption would not adversely affect safety, 3 seconds of total latency 

would provide a level of safety at least equal to that provided by the rule from which 

Army seeks the exemption: 

a. The U.S. Army UAS fleet have top speeds below 200 knots. Commercial airliners 

and fixed wing military aircraft fly at much faster speeds, usually at speeds exceeding 

400 knots, but they have the capability of flying even faster. It is understandable that 

fast moving aircraft must meet the 2-second latency requirement; however, a slow 

moving UAS that meets 3-second latency poses no safety threat. Since the latency 

requirement applies to a broad speed range; the DoD has assessed there is room for 

some leniency without sacrificing safety. At our request, the FAA analyzed the impact 

of having 3-second latency for slow moving aircraft and compared it to fast movers in 

relation to today's safety margins provided by radars. 

b. The FAA's analysis determined there is no appreciable safety impact of relaxing 

the 2-second total latency to 3-seconds for slow moving aircraft. For uncompensated 

latency, the findings reinforced that 0.6-second uncompensated latency is critical to 

maintaining safety margins. The U.S. Army UAS aircraft will comply with the 

uncompensated 0.6-second latency requirement, which can be done with current 

architecture and avionics. 

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SFAE-AV 

SUBJECT: Petition For Exemption From The Total Latency Provision of 14 CFR (Code 

of Federal Regulation) Part 91.227 For U.S. Army Unmanned Aircraft 

5. A summary FAA can publish in the Federal Register is not applicable for this 

exemption. 

6. Additional information, views or arguments available to support Army's request: 

a. In most U.S. Army UAS, both the aircraft position source(s) and the transponder 

are connected and communicate via a Mii-Std-1553 bus. The updated transponder will 

support ADS-B Out via both 1553 and ARINC-429 ports. Utilizing the current 

architecture and avionics per aircraft, ADS-B Out compliance to a 3-second latency limit 

could be accomplished by software upgrade to the avionics boxes. Army Aviation has 

programmed funding for ADS-BOut integration for the following platforms: RQ-7 and 

MQ-1C. Our funding will allow us to meet the 0.6-second uncompensated latency and 

total 3-second latency limit. 

b. If the Army UAS have to meet the 2-second latency limit, Army aviation will have 

to explore other engineering options such as upgrading processors, or putting the 

Global Positioning System (GPS) and Common Transponder (CXP) on the same bus, 

or directly connecting the GPS and CXP via ARINC-429 ports. The architectural 

modifications for any of these options are more extensive than were originally planned 

or budgeted for. Additionally, some of these options could require installation A-kits to 

be developed, as well as installed and formally tested. Consequently, the additional 

expense to modify all UAS Army platforms to meet the 2-second latency requirement is 

more than what was previously planned or budgeted for. If there was a safety concern, 

this additional expense would be necessary; however, for slow moving UAS aircraft the 

FAA has already agreed that 3-second latency does not pose an appreciable safety 

issue, so this additional expense is not justifiable. 

c. If Army UAS aircraft are allowed to meet ADS-B Out compliance to a 3-second 

total latency limit, the vast majority of our fleet can be compliant by the January 2020 

mandate. In contrast, if we have to meet the 2-second .total latency limit, because of the 

development and integration of installation kits and more extensive aircraft 

modifications, there is a high likelihood that many U.S. Army aircraft may not make the 

January 2020 ADS-B Out equipage mandate. 

7. Army will want to exercise the privileges of the exemption outside the United States 

because the U. S. Army has requirements to fly outside the United States. 

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SFAE-AV 

SUBJECT: Petition for Exemption From The Total Latency Provision of 14 CFR (Code 

of Federal Regulation) Part 91.227 For The U.S. Army Unmanned Aircraft 

8. Points of contact: 

a. PM Aviation Mission Equipment, Jeff Watteau, APM Surveillance, COMM (256) 

876-3358, DSN 746-3358, or e-mail jeffrey.a.watteau.civ@mail.mil. 

b. DoD NextGen Lead Service Office, COL Philip Basso, COMM (202) 404-7129, or 

e-mail philip.basso@pentagon.af.mil. 

nll~tJ~w ~o E"RT L. M~ION Brigadier General, USA 

Program Executive Officer, Aviation 

CF: Commander, U.S. Army Aeronautical Service Agency; 9325 Gunston Road, 

Bldg 1466, Suite N319; Fort Belvoir, VA 22060-5582 

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