On the night of January 18, 2003, the pilot of a Piper Cherokee learned a hard lesson about correct altimeter settings when his airplane hit the water off the coast of Orcas Island, Washington. He was seriously injured while one of his passengers died. The airplane was destroyed.
Just prior to taking off from Sequim Valley Airport, the pilot set the altimeter to the field elevation instead of setting the current barometric pressure in the pressure window. After contacting air traffic control, the pilot was informed of radar contact, given the current altimeter setting of 30.18, and told he was passing through 2,500 feet. The pilot then adjusted his altimeter to read 2,500 feet (30.50 in the pressure window) to match the ATC altitude.
Approaching Orcas Island Airport, the pilot noticed a layer of low-level fog and flew over the airport from south to north. He continued to maneuver and started a descent, looking for a place to get below the fog. While his altimeter read 600 feet, he continued descending over the water. Because he could not see the surface, the pilot turned on the landing light and his passenger remarked that the water looked close. Immediately, after the left wing hit the water, the pilot pulled up rapidly and added full power. The airplane did not have enough time to climb, striking the water, and cartwheeling into the channel.
At the time of the accident, the private pilot had accumulated 292 hours total time and 28 hours at night.
The NTSB determined the cause of this accident was the pilot's failure to maintain clearance from the water and his failure to reset the altimeter to the local barometric pressure. Contributing factors were fog and the night conditions.
The barometric setting of 30.50 inches results in an altitude difference of 330 feet when compared to the local altimeter setting of 30.17.
Altimeters have an adjustable pressure window for a reason. FAR 91.121 specifies that when operating below 18,000 msl, cruising altitude will be maintained by reference to an altimeter that is set to:
This pilot had multiple opportunities to prevent this accident. His departure airport had an ASOS, he was given the barometric pressure by ATC, and two nearby airports also had ASOS and ATIS reports available.
It is important to realize that even the smallest checklist item can have a huge effect on a flight's outcome. Remember that routine procedures, such as setting your altimeter, are the easiest to overlook. However, they are the most important and can make the difference in the safe outcome of a flight.
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This accident report as well as others can be found in the AOPA Air Safety Foundation's Online Database.
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