Narrative:

How problem arose: I worked all afternoon to inspect aircraft and prepare for an early morning departure, so I wanted to run up the engine before I went home. I taxied out to runup pad while the sun was still above the horizon. At this time there were distant clouds on the horizon blocking what I estimate was at least 30 mins (clock time) worth of sun travel before actual (legal) sunset. The actual 'legal' sunset time was critical because I operate aircraft without electrical system, therefore, without lights. I taxied back to the hangar and shut down at a time I estimated to be just before sunset behind the distant clouds. At this point, the sky was very bright, there was a full moon which had risen during the bright afternoon, and I could easily see aircraft on the ground 1 1/2 or 2 mi away on the other side of the airport, and aircraft in the sky were visible many mi away. After I shut down, the other pilots in the hangar and I were dumbfounded when an individual showed up, idented himself as an FAA official, and said that he thought that I taxied the aircraft after legal sunset. This started a lot of thought and debate within the other pilots in the hangar about safety, which leads to the following human factors considerations: should there be a visibility requirement for operating aircraft without lights, rather than an arbitrary rule about sunrise and sunset? If operating rules require day-by-day knowledge of local sunrise and sunset times, shouldn't they be published in the FARS and aim? The reference 'american air almanac' is not available at any fbos locally, or even at a local aerospace company flight operations center, nor did the 'FAA official' have one. I would be interested in any studies which show how much contrast is required for pilots to detect other aircraft on the ground without lights. I would think that contrast data could be used to derive visibility requirements to taxi aircraft without lights (I suspect that a few hundred ft would be safe for taxi) and to operate on runways (I suspect that a mi or more is required for runway operations). In the meantime I worry that ambiguity about local sunset will distract pilots from the real issue of adequate light/contrast/visibility for safety.

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Original NASA ASRS Text

Title: SMA BIPLANE OPERATED IN VIOLATION OF FAR 91 PT 209 IN THAT HE MOVED HIS ACFT DURING THE PERIOD AFTER OFFICIAL SUNSET WITHOUT POS LIGHTS. FARS.

Narrative: HOW PROBLEM AROSE: I WORKED ALL AFTERNOON TO INSPECT ACFT AND PREPARE FOR AN EARLY MORNING DEP, SO I WANTED TO RUN UP THE ENG BEFORE I WENT HOME. I TAXIED OUT TO RUNUP PAD WHILE THE SUN WAS STILL ABOVE THE HORIZON. AT THIS TIME THERE WERE DISTANT CLOUDS ON THE HORIZON BLOCKING WHAT I ESTIMATE WAS AT LEAST 30 MINS (CLOCK TIME) WORTH OF SUN TRAVEL BEFORE ACTUAL (LEGAL) SUNSET. THE ACTUAL 'LEGAL' SUNSET TIME WAS CRITICAL BECAUSE I OPERATE ACFT WITHOUT ELECTRICAL SYS, THEREFORE, WITHOUT LIGHTS. I TAXIED BACK TO THE HANGAR AND SHUT DOWN AT A TIME I ESTIMATED TO BE JUST BEFORE SUNSET BEHIND THE DISTANT CLOUDS. AT THIS POINT, THE SKY WAS VERY BRIGHT, THERE WAS A FULL MOON WHICH HAD RISEN DURING THE BRIGHT AFTERNOON, AND I COULD EASILY SEE ACFT ON THE GND 1 1/2 OR 2 MI AWAY ON THE OTHER SIDE OF THE ARPT, AND ACFT IN THE SKY WERE VISIBLE MANY MI AWAY. AFTER I SHUT DOWN, THE OTHER PLTS IN THE HANGAR AND I WERE DUMBFOUNDED WHEN AN INDIVIDUAL SHOWED UP, IDENTED HIMSELF AS AN FAA OFFICIAL, AND SAID THAT HE THOUGHT THAT I TAXIED THE ACFT AFTER LEGAL SUNSET. THIS STARTED A LOT OF THOUGHT AND DEBATE WITHIN THE OTHER PLTS IN THE HANGAR ABOUT SAFETY, WHICH LEADS TO THE FOLLOWING HUMAN FACTORS CONSIDERATIONS: SHOULD THERE BE A VISIBILITY REQUIREMENT FOR OPERATING ACFT WITHOUT LIGHTS, RATHER THAN AN ARBITRARY RULE ABOUT SUNRISE AND SUNSET? IF OPERATING RULES REQUIRE DAY-BY-DAY KNOWLEDGE OF LCL SUNRISE AND SUNSET TIMES, SHOULDN'T THEY BE PUBLISHED IN THE FARS AND AIM? THE REF 'AMERICAN AIR ALMANAC' IS NOT AVAILABLE AT ANY FBOS LOCALLY, OR EVEN AT A LCL AEROSPACE COMPANY FLT OPS CENTER, NOR DID THE 'FAA OFFICIAL' HAVE ONE. I WOULD BE INTERESTED IN ANY STUDIES WHICH SHOW HOW MUCH CONTRAST IS REQUIRED FOR PLTS TO DETECT OTHER ACFT ON THE GND WITHOUT LIGHTS. I WOULD THINK THAT CONTRAST DATA COULD BE USED TO DERIVE VISIBILITY REQUIREMENTS TO TAXI ACFT WITHOUT LIGHTS (I SUSPECT THAT A FEW HUNDRED FT WOULD BE SAFE FOR TAXI) AND TO OPERATE ON RWYS (I SUSPECT THAT A MI OR MORE IS REQUIRED FOR RWY OPS). IN THE MEANTIME I WORRY THAT AMBIGUITY ABOUT LCL SUNSET WILL DISTRACT PLTS FROM THE REAL ISSUE OF ADEQUATE LIGHT/CONTRAST/VISIBILITY FOR SAFETY.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.