The Anti-Collision Light is Inop but the strobes work. Am I legal to fly?

By Darrell W. Contreras, Esq., CFI, MEI

You are finally scheduled to fly and the weather is beautiful for a day VFR flight.  You get to the airport and preflight the plane.  During your preflight, you notice that the anti-collision light does not work.  There are wingtip strobes installed on the plane and those work.  Is that enough?  Do you need both?  Is the plane still legal to fly?  This exact question was addressed in an FAA Letter of Interpretation requested by Thomas D. Letts and dated December 19, 2017 under the heading:  “Request for Legal Interpretation Regarding the Operation of an Aircraft Equipped with an Inoperative Rotating Beacon”.

A Letter of Interpretation is an official response from the FAA to clarify the application of one or more regulations to a specific fact pattern.  In this Letter, the issue was, “whether a Cessna 172, equipped with a red rotating beacon and white strobe lights, may be operated using only the white strobe lights if the red rotating beacon is inoperative, placarded as ‘INOP,’ and the appropriate entry has been made in the aircraft logbook.”  The short answer provided by the FAA in the Letter of Interpretation was operation of the aircraft in such condition would not be permitted.  To understand the basis for this conclusion, we need to review the regulations and the history behind the regulations.

When we think of required equipment for VFR day flight, we immediately turn to the Federal Aviation Regulations (FAR) section 91.205(b) and our “A TOMATO FLAMES” acronym.  However, when it comes to the question of the operational status of one or both of the strobe and anticollision lights, the answer is much more complicated.

FAR section 91.205(b) reads:  Visual-flight rules (day). For VFR flight during the day, the following instruments are required:


(11) For small civil airplanes certificated after March 11, 1996, in accordance with part 23 of this chapter, an approved aviation red or aviation white anticollision light system. In the event of failure of any light of the anticollision light system, operation of the aircraft may continue to a location where repairs or replacement can be made.

If we stop there, we would look to the date of certification of the airplane and if it was before 1996, we would conclude that an anticollision light system is not required for day VFR flight. Not exactly.  This may be tricky, but here is the basic explanation:  This rule requires an anti-collision light for airplanes certificated after March 11, 1996 but it does not state that airplanes certificated prior to March 11, 1996 are excluded.

Any time you see a date associated with a regulation, you need to ask why.  Frequently, the date listed corresponds to the date a new or changed regulation was enacted and there was a specific reason for that change.  To find the explanation for the change, you would need to look to the history of 91.205(b)(11) and the discussion of proposed changes to regulations contained in the Notice of Proposed Rulemaking (NPRM).  An NPRM is a fancy title that means changes to regulations are coming out, provides an explanation of why the changes are being issued, and invites public comments on the proposed changes.  In the discussion of the anti-collision light system and a review of the reports of midair accidents that occurred in day VFR conditions, the FAA stated, “Requiring the installation of anticollision lights on all newly certificated airplanes and, as proposed by revised § 91.209 in this notice, requiring operation of anticollision lights during day operations would increase the airplane’s conspicuity and contribute to a reduction in the number of accidents.” (59 FR 37629; July 22, 1994).

What this tells us is when the regulation was published, the FAA was focused on reducing the number of day VFR midair accidents and it believed that having an operating anticollision light would help address the problem.  That conclusion was stated in the NPRM:  “Even if such action is only 25 percent effective, a review of the 6-year service history indicates that approximately 17 fatalities could be avoided in a similar 6-year period.” (59 FR 37629; July 22, 1994).  As a result, the March 11, 1996 date corresponds to when the FAA implemented rules to require pilots to use the anticollision light during day VFR conditions.

Now that we know why, let’s look at how it all fits together.  Did you notice the reference to 91.209 in the FAA statement above?  This NPRM included proposed revisions to FAR section 91.209, the relevant section for this discussion is (b), which states, “No person may: … (b) Operate an aircraft that is equipped with an anticollision light system, unless it has lighted anticollision lights. However, the anticollision lights need not be lighted when the pilot-in-command determines that, because of operating conditions, it would be in the interest of safety to turn the lights off.”  (59 FR 37643; July 22, 1994).  In addition, the NPRM included proposed revisions to FAR section 91.205(b) that added paragraph (b)(11), the day VFR requirement for an anticollision light system for airplanes certificated after March 11, 1996.  This means:

  1. If your airplane was certificated after March 11, 1996, then an anticollision light system is required for day VFR operations; AND
  2. Regardless of when your airplane was certificated, FAR section 91.209(b) requires the anticollision light system to be operating if the airplane is so equipped.

The FAA considered that most airplanes were built for night operations, for which an anticollision light system was already required, meaning the system was already installed on the airplane.  Because of that, it is clear that the FAA’s objective with this revision was to require pilots to operate the anticollision light system during day VFR conditions.

We now understand that the FAA believes that safety is enhanced with the use of the anticollision light system during day VFR conditions, but what if the “anticollision light system” includes a tail beacon and a strobe, and one of them is not operational?  This was the question submitted in the original Letts letter that resulted in this FAA Letter of Interpretation.

The original Letts letter pointed out that FAR section 91.205(b)(11) reads, “an approved aviation red OR aviation white anticollision light system.” The Letts letter considered the aviation red tail beacon and the aviation white strobe lights as separate systems.  Therefore, the Letts letter concluded, as long as one of the “systems” is operational, the regulation is satisfied.  The FAA disagreed, basing its decision on a January 11, 2011 legal interpretation letter from Rebecca MacPherson, Assistant Chief Counsel for Regulations, to Mr. Daniel Murphy.  That legal interpretation cited FAR 23.1401(a)(1), which reads:  “[t]he airplane must have an anticollision system that…consists of one or more approved anticollision lights…” The legal interpretation then concluded that one or more means a single system can include both the strobe light and the rotating beacon stating, “Because the strobe light and the rotating beacon are both approved anticollision lights under §23.1401(a)(1), they are both part of the same anticollision system.”  The Letter of Interpretation to Letts then affirmed the conclusion of the 2011 legal interpretation that the strobe light and rotating beacon are one and not two systems stating, “the FAA considers the aircraft’s rotating beacon and strobe lights to be part of the aircraft’s anticollision light system.”  Therefore, because an anticollision system is comprised of one or more approved anticollision lights, and because both the rotating beacon and the strobe lights are approved anticollision lights, they are part of the same system.  If both lights are part of the same system, then the word, “or” in FAR section 91.205(b)(11) does not apply to the rotating beacon and the strobe lights and means both must be operational if installed.  As a result, the FAA concluded, “both the rotating beacon and strobe lights would need to be operable for the requirements of § 91.205 to be met.”

The end result of all of this is your perfect day for flying is can only proceed if the entire installed anticollision light system, rotating beacon and strobe lights, is operational.  With only one of the two operational, your perfect day of flying is unfortunately grounded.

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