Sunday, April 28, 2019

Piper PA-18-150, registered to and operated by Brooks Flyers LLC as a visual flight rules (VFR) aerial observation flight under the provisions of 14 Code of Federal Regulations (CFR) Part 91, N83641: Accident occurred November 22, 2016 in Bethel, Alaska

The National Transportation Safety Board did not travel to the scene of this accident.

Additional Participating Entity:
Federal Aviation Administration / Flight Standards District Office; Anchorage, Alaska

Aviation Accident Factual Report - National Transportation Safety Board:

Investigation Docket - National Transportation Safety Board:

Location: Bethel, AK
Accident Number: ANC17LA007
Date & Time: 11/22/2016, 1400 AKS
Registration: N83641
Aircraft: PIPER PA-18
Aircraft Damage: Substantial
Defining Event: Powerplant sys/comp malf/fail
Injuries: 2 None
Flight Conducted Under: Part 91: General Aviation - Aerial Observation 

On November 22, 2016, about 1400 Alaska standard time, a Piper PA-18-150 (Super Cub) airplane, N83641, sustained substantial damage during an emergency landing near Bethel, Alaska. The airplane was registered to and operated by Brooks Flyers LLC, as a visual flight rules (VFR) aerial observation flight under the provisions of 14 Code of Federal Regulations (CFR) Part 91 when the accident occurred. The certificated commercial pilot and one passenger were uninjured. Visual meteorological conditions prevailed, and company flight following procedures were in effect. The flight departed Bethel, at about 1050 with an intermediate stop at a remote unimproved landing site.

In a statement provided to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the pilot stated that the purpose of the flight was to conduct wildlife surveys for the Alaska Department of Fish and Game. He stated that about 2 hours and 40 minutes into the flight they landed on a remote gravel bar to take a break, followed by departure and climb-out a few minutes later. During the climb, he noticed his oil pressure had redlined at 100 pounds per square inch (psi) with an oil temperature of 138 degrees Fahrenheit. In an effort to correct for the high oil pressure, he reduced his power to 2150 RPM and the oil pressure came down to 90 psi, with all other engine instruments in the normal range. He adjusted his course for Bethel while slowly climbing the airplane to about 1,000 feet above ground level, and applied the carburetor heat. Shortly thereafter, smoke began filling the cockpit. He turned into the wind, applied full flaps, reduced the power to idle, and selected a small frozen lake as an emergency landing site. While maneuvering for the emergency landing the engine lost all the power, and he made a forced landing in an area of tundra covered terrain. During the forced landing the airplane sustained substantial damage to the left wing.

On February 24, 2017, the NTSB IIC, along with another NTSB investigator examined the engine and propeller at the facilities of Alaska Claims Services, Inc., Wasilla, Alaska. The propeller remained attached to the engine crankshaft. Both of the propeller blades exhibited torsional "S" twisting, and minor chordwise scratching. Examination of the Lycoming O-360-A1A engine revealed no anomalies, contamination, or evidence of malfunction in any of the engine accessories. The cylinders, pistons, valve train, crankshaft, and other internal components were all without evidence of anomaly or malfunction. However, no oil was present on the engine oil dipstick, and the crankshaft oil seal or nose seal was displaced, and evidence of oil was apparent under and around the displaced seal.

Further examination revealed that the engine breather tube was not insulated, and did not have a "whistle slot" located in a warm area on the breather tube.

During a telephone conversation on May 12, 2017 the mechanic who maintained the airplane stated that the engine breather tube had been replaced about 2 years prior to the accident during an engine conversion, and he must have forgot to put the hole (whistle slot) in the tube at that time.

Lycoming Engines website, Contact and Support, Knowledge Base, Tips, "How to Avoid a Nose Seal Leak" states in part: "To avoid the problem of oil leakage at the crankshaft oil seal because of an engine breather restriction, examination of the breather tube to determine its condition is an excellent idea. If the tube is in good condition, also remember that the engine expels moisture through the tube. Under freezing conditions, there is some possibility that the moisture may freeze at the end of the tube and ice will build up until the tube is completely restricted. Should this happen, pressure may build up in the crankcase until something gives – usually the Crankshaft Oil Seal.

Since the airframe manufacturers know this is a possibility, and since they design with the intention of preventing engine-related problems of this kind, some means of preventing freeze-up of the crankcase breather is usually a part of the aircraft design. The breather tube may be insulated, it may be designed so the end is located in a hot area, it may be equipped with an electric heater, or it may incorporate a hole, notch or slot which is often called a "whistle slot." Because of its simplicity, the whistle slot is often used and is located in a warm area near the engine where it will not freeze. Aircraft operators should know which method of preventing freeze-up is used and then ensure that the configuration is maintained as specified by the airframe manufacturer."

The closest weather reporting facility was Bethel Airport, Bethel, Alaska, about 45 miles south of the accident site. At 1353, an Aviation Routine Weather Report (METAR) from Bethel Airport was reporting, in part: wind from 020 degrees at 10 knots; visibility, 6 statute miles, mist; clouds and sky condition, few clouds at 15,000 feet, few clouds at 25,000 feet; temperature, 0 degrees F; dew point -2 degrees F; altimeter, 29.41 inHG.

Pilot Information

Certificate: Commercial
Age: 33, Male
Airplane Rating(s): Single-engine Land; Single-engine Sea
Seat Occupied: Front
Other Aircraft Rating(s): None
Restraint Used: 4-point
Instrument Rating(s): Airplane
Second Pilot Present: No
Instructor Rating(s): None
Toxicology Performed: No
Medical Certification: Class 2 Without Waivers/Limitations
Last FAA Medical Exam: 01/07/2016
Occupational Pilot: Yes
Last Flight Review or Equivalent: 04/18/2016
Flight Time:  5170 hours (Total, all aircraft), 1400 hours (Total, this make and model), 5145 hours (Pilot In Command, all aircraft), 187 hours (Last 90 days, all aircraft), 49 hours (Last 30 days, all aircraft), 2 hours (Last 24 hours, all aircraft)

Aircraft and Owner/Operator Information

Aircraft Make: PIPER
Registration: N83641
Model/Series: PA-18
Aircraft Category: Airplane
Year of Manufacture: 1977
Amateur Built: No
Airworthiness Certificate: Normal
Serial Number: 18-7709109
Landing Gear Type: Tailwheel
Seats: 2
Date/Type of Last Inspection: 09/01/2016, 100 Hour
Certified Max Gross Wt.: 1750 lbs
Time Since Last Inspection:
Engines: 1 Reciprocating
Airframe Total Time: 5133.2 Hours at time of accident
Engine Manufacturer: LYCOMING
ELT: C91  installed, not activated
Engine Model/Series: O-360 SERIES
Registered Owner: BROOKS FLYERS LLC
Rated Power: 180 hp
Operating Certificate(s) Held: On-demand Air Taxi (135)

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual Conditions
Condition of Light: Day
Observation Facility, Elevation: PABE
Distance from Accident Site: 45 Nautical Miles
Observation Time: 2253 UTC
Direction from Accident Site: 171°
Lowest Cloud Condition: Few / 15000 ft agl
Visibility:  6 Miles
Lowest Ceiling: None
Visibility (RVR):
Wind Speed/Gusts: 10 knots /
Turbulence Type Forecast/Actual: /
Wind Direction: 20°
Turbulence Severity Forecast/Actual: /
Altimeter Setting: 29.41 inches Hg
Temperature/Dew Point: -18°C / -19°C
Precipitation and Obscuration: Moderate - Mist
Departure Point: Bethel, AK
Type of Flight Plan Filed: Company VFR
Destination: Bethel, AK
Type of Clearance: VFR
Departure Time:  AKS
Type of Airspace: Class G

Wreckage and Impact Information

Crew Injuries: 1 None
Aircraft Damage: Substantial
Passenger Injuries: 1 None
Aircraft Fire: None
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries: 2 None
Latitude, Longitude: 61.414722, -161.958056 (est)

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