Perils of Flat Light
The U.S. National Transportation Safety Board reported that according to the front-seat passenger of a Bell 206L, there was no visible horizon, and everything was just all gray. He also stated that it was snowing, the water was flat and it was hard to tell where the water ended and the sky began. He further stated that although he could not tell exactly how high above the water they were, it was a lot lower than he thought they should be. At one point, they got low enough that the passenger could see a white spray off the top of the water where the force of the wind from the main rotor whipped up the surface.
Then, according to this witness, the skids either entered the water or skipped a couple of times across its surface. Almost immediately after the skids contacted the water, the helicopter's nose came up, its tail appeared to hit the water, and the aircraft quickly pulled away from the surface. Immediately thereafter, the nose dipped forward and the pilot seemed to be rapidly moving the controls all over the place. The helicopter began to rotate as it descended, impacting the water very hard.
Another passenger seated in the forward-facing right rear seat stated he was real uncomfortable with the low altitude, and wanted to say something to the pilot, but did not because he was concerned that he would break the pilot's concentration. He said the water was calm and flat, and that it was very hard to tell exactly how high above the surface they were. He said that, although he was uncomfortable with the aircraft flying at what looked to him to be just above the surface of the water, there was otherwise nothing unusual about the movements or the flight path of the helicopter until the skids touched the water.
This accident happened on Oct. 18, 2001 while attempting to cross Cook's Inlet en route to Anchorage, Alaska. At the time the pilot called Anchorage Tower to request a Special VFR clearance, the ATIS reported the wind was variable at 5 kt. and the visibility was 1 mi. with light snow and mist. There was a broken ceiling at 400 ft., a broken layer at 1,700 ft., and a 3,400-ft. overcast layer. Temperature and dew point were 0C and -1C respectively.
The airport surface weather observation about 10 min. after the accident indicated calm winds, 3/4 mi. visibility, light snow and mist, a vertical visibility of 800 ft., with a remark that visibility from the tower was 1 mi..
The pilot held a helicopter commercial pilot certificate, but was not instrument rated. According to his employer's records, he had completed inadvertent IMC training several months prior to the accident and had accumulated more than 10,000 pilot hours in helicopters, 8,000 of which were in the Bell 206. He and two other passengers were fatally injured in the crash.
A short flight crossing a body of water in bad weather might seem like a safe alternative to scud running over land. However, flying low over water can quickly turn into a complete loss of visual clues (commonly referred to as white-out conditions). This environment can cause pilots to lose their depth of field in vision and spatial orientation. When this condition exists during periods of flat light, all contrast is lost, requiring a quick change to instruments and a possible climb to get away from the surface. For a pilot not proficient with instruments, this becomes a no-way-out situation.
Flat-light conditions can exist during periods of good visibility and create an inability to distinguish distances and closure rates. Typically, overcast skies coupled with near featureless terrain or glassy water will produce a flat-light environment.
In fact, on March 21, 2002, with 30 mi. visibility and 18,000 ft. overcast skies, an Astar was crossing Honey Lake en route to Susanville, Calif. A flight nurse seated directly behind the ATP-rated pilot stated that the lake was like a mirror and reflected the clouds and the sky perfectly, and it was kind of mesmerizing and disorienting to see clouds both above and below. Looking out the right-side window at the distant shoreline he thought to himself that the flight seemed very low. The pilot said on the intercom, "Boy, it's disorienting when the lake is this smooth." The helicopter then hit the water, fatally injuring the pilot and seriously injuring the two medical crewmembers. Flying low to water just for the thrill can be tempting for some pilots. However, it's a risk not worth taking.
The FAA's Aviation Safety Program offers the following pilot-inspired techniques to lower flat-light risks: Always leave yourself an out. Do not fly until you have one visual reference left. Try not to lose sight of your reference point at any time. Fly with your head straight, looking forward, and believe your flight instruments. In addition, if you're not instrument-rated or experienced, set your personal minimums higher and stick to them. Failure to do so can easily have fatal consequences.
For more information on this topic and the Aviation Safety Program, visit www.faasafety.gov.