Pilot Counsel:

Anticollision lights

September 1, 2011

John YodiceIf an aircraft is equipped with an “anticollision light system,” as most modern aircraft are, a pilot must not “operate” that aircraft unless the system is lighted, or in other words, the anticollision lights are “on.” That’s the basic rule of FAR 91,209(b). Yet, there are two questions raised by the rule that we oftentimes hear debated in spirited hangar flying sessions. Now we have a recent interpretation of the FAA chief counsel that authoritatively answers these debates within the strict terms of the rule, but with important safety precautions.

One of the debates is about whether the lights must be on prior to engine start, or whether they can be delayed until after engine start. The interpretation focuses on the meaning of the word “operate” in the rule and goes on to conclude that the lights are not required to be on prior to engine start. The term “operate” is defined as “use, cause to use or authorize to use aircraft, for the purpose…of air navigation….” It is defined intentionally broadly to facilitate FAA enforcement of the operating and flight rules. It is intended to cover not only a pilot or an airline that is obviously an operator but others that may not be commonly understood to be operators of an aircraft. However, in the context of the anticollision lights regulation, the broad scope of the definition takes an interesting twist based on FAA past statements. In the past the FAA has taken the position that the term “operate” applies to “those acts which impart some physical movement to the aircraft, or involve the manipulation of the controls of the aircraft such as starting or running an aircraft engine.” And the FAA has also said that “an aircraft is being operated when its engine is turned on with the intent of using that aircraft to take off and engage in air navigation.” The implication of these statements is that an aircraft that is about to be used is not being operated until an engine is actually started.

Once that aircraft’s engine is started for the purpose of air navigation it is clear that FAR 91.209(b) requires that the aircraft’s anticollision lights be turned on.

It is important to note that this interpretation addresses what is specifically required by the rule. The FAA is quick to offer a safety precaution. The FAA recommends, as a matter of safety, that the anticollision lights should be on before starting an engine or causing a propeller or rotor to move. That is a common practice among many pilots.

Here is the second interesting question that is addressed by the FAA interpretation. Many aircraft have both an anticollision rotating beacon and an anticollision strobe light system. If the anticollision system is required to be on, must both the rotating beacon and the strobes be on? The answer is technically yes, but again with an important safety qualification.

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The answer is yes because the strobe light and the rotating beacon are considered part of the same anticollision system. However, the FAA does recognize the concern that the use of a strobe light as an anticollision light could create an unsafe condition during certain aircraft operations. The FAA agreed that the use of a high intensity anticollision light, such as a strobe light, could create unsafe conditions by inducing vertigo and causing spatial distortion. As a result the FAA included language in the rule to give the pilot in command the discretion to control how many lights are turned on in the anticollision system. The regulation permits the pilot in command to turn off the anticollision lights if he or she “determines that, because of operating conditions, it would be in the interest of safety to turn the lights off.” FAR 91.209(b), as interpreted, gives the pilot in command the discretion to turn off the anticollision beacon and/or the anticollision strobe light system if he/she determines that it is in the interests of safety.

So, for you hangar-flying lawyers, although it is ordinarily safer to turn on the anticollision lights prior to engine start, it is not required by FAR 91.209(b); and for aircraft that have both a rotating beacon and strobe lights, while both are part of the same anticollision light system, one or both can remain unlighted during aircraft operation, within the safety discretion of the pilot in command.

John S. Yodice is an instrument rated provate pilot and owner of a Cessna 310.