One of the NTSB's most recently published probable-cause reports, for a floatplane near Petersburg that killed one person last year, attributed the crash to pilot error which led to an aerodynamic stall.
The Federal Aviation Administration announced in February that it had simplified its requirements for general aviators to install angle-of-attack indicators in an effort to reduce stalling issues.
NTSB spokesperson Clint Johnson hailed the FAA's decision to remove some of the red tape that previously dissuaded pilots from installing the indicators in their planes.
"We applaud the FAA -- they've been able to streamline having this type of equipment," Johnson said. "Stalls are not uncommon, by any means; it's one of the first things you learn and try to avoid in primary flight training, so this type of equipment can only be for the better so we support this 110 percent."
Angle-of-attack indicators alert pilots when their wing position is getting too steep and they're close to stalling.
While many aircraft already have a stall warning horn, Northern Lights Avionics owner Gary Bennett says that's not always enough.
"Most certificated aircraft have a stall warning horn, and basically that's a horn that goes off in some cases when it's just too late," Bennett said.
Bennett says the concept of the angle-of-attack indicator isn't new, and has been in use with military aircraft and pilots for years.
"This actually is like looking over the pilot's shoulder, somebody giving 'em information about the lift that's underneath the wing, letting them know if they're getting too slow or having too much of a angle upon the landing, which makes them stall and ultimately fall out of the sky," Bennett said.
Bennett says the indicator's advantage over a warning horn is that it gives pilots more time to react.
"At least with the AOA indicator, you have an indication as you approach that point and (it) gives you pre-warnings before you actually hit the stall phase," Bennett said.
Mark Madden, the vice-chair of the Alaskan Aviation Safety Foundation, says he's currently having an angle-of-attack indicator installed on his personal plane. He says indicators could be a crucial tool in preventing stall-related crashes in Alaska, primarily during the hunting season. NTSB information has pointed to so-called "moose-turn stalls" by preoccupied hunters in at least two deadly crashes last year.
"We might have pilots flying around looking for subjects of interest -- such as maybe some rather large four-legged animals with really big antlers -- and they start to forget to fly the airplane," Madden said. "The angle-of-attack indicator won't get distracted."
An angle-of-attack indicator includes a probe that attaches to the wing of a plane, which senses airflow and warns the pilot of any problems.
"It adds one more layer of safety to your flying and when you consider the cost it's a great investment it'll return on your investment," Madden said.
Like many aviation-related tools indicators aren't cheap, ranging between $1,600 and $2,200 -- but aviation experts say if you can afford to buy it as a precaution, it could save your life.
According to AASF, 60 percent of all aircraft stalling events happen during takeoff or landing.
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NTSB Identification: ANC13FA054
Nonscheduled 14 CFR Part 135: Air Taxi & Commuter
Accident occurred Tuesday, June 04, 2013 in Petersburg, AK
Probable Cause Approval Date: 06/02/2014
Aircraft: DEHAVILLAND BEAVER DHC-2 MK.1, registration: N616W
Injuries: 1 Fatal,2 Serious,4 Minor.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The pilot reported that the accident flight was his fourth flight and the third tour flight of the day in a float-equipped airplane. The weather had deteriorated throughout the day with lowering ceilings, light rain, and fog on the mountain ridges. The pilot said that when approaching a mountain pass, he initiated a climb by adding a “little bit” of flap (about 1 pump of the flap handle actuator) but did not adjust the engine power from the cruise power setting. He noted his airspeed at 80 knots, with a 200-feet-per-minute climb on the vertical speed indicator. He was having difficulty seeing over the cowling due to the nose-high attitude, when he suddenly noticed trees in his flight path. He initiated an immediate left turn; the airplane stalled, and began to drop, impacting the mountainous, tree-covered terrain.
A passenger reported that the weather conditions at the time of the accident consisted of tufts of low clouds, and good visibility. They did not enter the clouds at any time during the flight. He reported that the airplane made a left turn, stalled, and then made a sharp left turn right before impact. The airplane seemed to be operating fine, and he heard no unusual sounds, other than the engine speed seemed to increase significantly right before impact.
The pilot reported that there were no preaccident mechanical anomalies that would have precluded normal operation, and the postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.
The National Transportation Safety Board determines the probable cause(s) of this accident to be:
The pilot’s failure to maintain adequate altitude above the trees, and his subsequent failure to maintain adequate airspeed while maneuvering to avoid the trees, which resulted in an inadvertent aerodynamic stall/spin and an uncontrolled descent.
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