Three aircraft crashes earlier this week in two mountainous areas outside of Anchorage, Alaska emphasize to pilots the importance of constant situational awareness and proper weather and flight planning. The first crash occurred on August 8 about 8,500 feet up Knik Glacier, approximately forty miles northeast of Anchorage, and involved a Piper PA-32 aircraft on a sightseeing tour. The pilot reported hitting a downdraft that caused the plane to hit the side of the glacier. In one interview, the pilot reported that the incident seemed surreal because even though he had established climb power and had a nose up attitude, the plane’s altimeter indicated a significant descent. Fortunately, of the five people aboard, only two sustained minor injuries.

The second crash arose from the same incident but involved an Alaska Air National Guard HH-60 helicopter that was attempting to rescue the sightseers stranded on the glacier. At some point during the operation, the helicopter slid on the glacier and rolled for a short distance. The pilot of the downed PA-32 stated that it looked to him like the helicopter also hit a downdraft. None of the crew members aboard the helicopter were injured.

The third crash happened the next day near Dillingham, Alaska and involved a DeHavilland DHC-3T Otter aircraft. This crash has received a great deal of press coverage because it killed five people, including former U.S. Senator Ted Stevens, and critically injured four others, including former NASA chief Sean O’Keefe.

The cause of this crash is currently being investigated by the NTSB and there is currently not much information available, so no one can say for certain at this point why the plane went down. There are, however, a couple of possibilities, which, even if are ultimately determined to be unrelated to the crash, are worth a few minutes of every pilots’ thoughts.

First, it seems likely that a mountain downdraft, also known as a mountain wave, caused the first plane to crash on Knik Glacier, and may have caused or contributed to the crash of the rescue helicopter. It is also very possible that a downdraft caused the crash of the plane that killed Senator Stevens. Indeed, the ground scar leading up the mountain to the plane’s wreckage could be quite consistent with that scenario.

According to the Aeronautical Information Manual (AIM), “mountain waves occur when air is being blown over a mountain range or even the ridge of a sharp bluff area.” The air hitting the upwind side of the mountain rises and generally causes a smooth updraft. The smooth updraft, however, often turns into a violent downdraft as the air passes the crest of the ridge. The AIM further states that “all it takes to form a mountain wave is wind blowing across the range at 15 knots or better at an intersection angle of not less than 30 degrees.”

In order to safely fly in mountainous areas, the AIM recommends that when flying on the leeward side of a mountain always expect a downdraft and always add an extra thousand feet or so of altitude above ground level because, just as the pilot of the PA-32 discovered, “downdrafts can exceed the climb capability of the aircraft.” The AIM also recommends that approaches to a mountain ridge from the downwind side should be made at about a 45 degree angle to the horizontal direction of the ridge. This allows for a safer retreat from the ridge if necessary. One should also always be prepared for significant turbulence when flying near mountains.

Another possible cause of the DHC-3T Otter crash in Alaska is an unexpected encounter with fog or clouds. According to news accounts, the aircraft was on a VFR flight plan at the time of the crash. As experienced pilots know, however, when flying in mountains fog can accumulate in valleys very quickly and clouds banks can move in just as quickly to obscure the surrounding terrain. The AIM defines the later situation as Mountain Obscuration (MTOS) and it can be quite dangerous for obvious reasons. In mountainous areas, the ground level can vary greatly over small distances and with the mountain tops being obscured, a pilot encountering sudden MTOS may well be in immediate danger of flying into the terrain.

An additional danger associated with MTOS, as with all inadvertent flight into IMC conditions, is disorientation. The sudden loss of ground references and the shift from visual cues outside the cockpit to complete reliance on instruments can have an adverse effect on even the most seasoned pilots. Thus, pilots should frequently review and practice their procedures for minimizing and responding to disorientation situations.

Avoidance of all of the dangers mentioned above involves proper flight planning, proper in-flight execution, good judgment and constant situational awareness. No amount of experience makes a pilot immune from the necessity of reviewing and practicing the basics, and perhaps the most basic thing for any pilot to remember is that Mother nature is always in charge. Ignore her at your own risk.

William Angelley is a former navy Pilot, aviation attorney and Partner in the law firm of Hightower Angelley LLP. His firm web address is www.hightangel.com.