Saturday, May 15, 2021

Loss of Control in Flight: Piper PA-25-260 Pawnee, N4369Y; fatal accident occurred August 27, 2015 near Crystal Airport (46CN), Llano, Los Angeles County, California

Channing Morse

Aviation Accident Final Report - National Transportation Safety Board 

The National Transportation Safety Board traveled to the scene of this accident

Additional Participating Entities: 

Federal Aviation Administration /  Flight Standards District Office; Van Nuys, California 
Lycoming Engines; Williamsport, Pennsylvania 

Investigation Docket - National Transportation Safety Board:

Location: Llano, California 
Accident Number: WPR15FA250
Date & Time: August 27, 2015, 12:06 Local
Registration: N4369Y
Aircraft: Piper PA 25
Aircraft Damage: Substantial
Defining Event: Loss of control in flight 
Injuries: 1 Fatal
Flight Conducted Under: Part 91: General aviation - Glider tow


The tow plane pilot had performed six uneventful glider launches on the morning of the accident with turnaround times of about 15 minutes. The seventh launch was uneventful, and, after releasing the glider, the pilot made an appropriate radio call and was observed normally entering the downwind traffic pattern. Video data and witness accounts indicated that, shortly after, the airplane descended well below pattern altitude and overshot the runway centerline by about 1/4 mile during the turn from the base leg to final approach. The airplane then began to maneuver erratically as it passed back across the centerline, and subsequently collided in a dirt field 900 ft southwest of the threshold of the gravel portion of the runway.

Postaccident examination of the airframe and engine did not reveal any anomalies that would have precluded normal operation, and the engine data monitor information indicated that the engine performed similarly for all of the flights on the day of the accident, including the accident flight.

The pilot was issued a second-class medical certificate 6 days before the accident. At that time, he reported having high blood pressure, which had been controlled with medication for many years. Two years before the accident, he had taken a cardiac stress test, which had to be stopped prematurely due to shortness of breath. Further, his wife reported that he had a bout of unusual dizziness while hiking on a hot day about 1 year before the accident.

The autopsy revealed hypertrophic heart disease, a condition associated with an increased risk of developing atrial fibrillation, an arrhythmia that typically causes a fast heart rate, which may lower blood pressure, even to the point of causing fainting. Onset of atrial fibrillation is typically sudden. It was a hot day, and there may have been a component of sweating and heat effects, particularly during the periods when the airplane was on the ground, which may have increased the amount of physiologic stress and the likelihood of an arrhythmia. The sudden onset of an arrhythmia can cause symptoms ranging from palpitations to loss of consciousness but leaves no evidence after death.

The lack of mechanical problems, the pilot's successful completion of six tow flights before the accident flight, the radar track, and the pilot's failure to make a radio call regarding an emergency are consistent with sudden incapacitation, and it is likely the pilot's incapacitation caused the accident. 

Probable Cause and Findings

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
The pilot's loss of airplane control during the landing approach due to an incapacitating medical event.


Personnel issues Cardiovascular - Pilot
Personnel issues Aircraft control - Pilot

Factual Information

History of Flight

Approach-VFR pattern base Loss of control in flight (Defining event)
Approach-VFR pattern base Collision with terr/obj (non-CFIT)

On August 27, 2015, at 1206 Pacific daylight time, a Piper PA-25-260, N4369Y, collided with terrain during the landing approach to Crystal Airport, Llano, California. The airline transport pilot was fatally injured, and the airplane sustained substantial damage. The airplane was registered to, and was being operated by, Southern California Soaring Academy (SCSA), Inc., as a 14 Code of Federal Regulations Part 91 glider tow operation. Visual meteorological conditions were reported about the time of the accident near the accident site, and no flight plan had been filed. The local flight departed at 1150.

Glider tow operations began at 1025 on the day of the accident, and 19 flights were planned in the tow plane throughout the day. The accident pilot was assigned to fly through early afternoon, and a second pilot was going to take over later in the day. Right downwind arrival procedures for runway 25 were in effect for glider traffic. The procedures called for the next glider in the launch sequence to be moved from the northeast staging area to runway 25 when traffic permitted and to depart in tow from the 2,600-ft-long tarmac runway. The tow plane was then to use the runway 7 right downwind approach for a landing in the opposite direction, on the "Tow Plane Landing Zone," which was a parallel gravel surface adjacent to runway 7.

The tow pilot completed six uneventful launches before the accident with turnaround times of about 15 minutes. After the sixth launch, the tow plane was serviced with 26 gallons of fuel.

For the accident flight, the tow plane departed with the glider, headed south of the airport, and released from the glider in the foothills of the San Gabriel Mountain Range in an area known within the SCSA as the "Second Ridge." The pilot flew the tow plane the 4 miles back to the airport. Multiple witnesses at the airport reported hearing the pilot report over the common traffic advisory frequency that he was entering the right traffic pattern for runway 7. About that time, another glider was approaching the airport from the north, and it had entered the right downwind leg for runway 25. The glider pilot continued his approach, and along with several other witnesses, heard the tow pilot make appropriate position calls as his approach progressed.

The glider landed just beyond the runway threshold. The glider pilot reported that, during the landing rollout, he was surprised to see the tow plane now north of the airport, abeam the approach end of runway 7, flying in a steep 70 to 80° right bank such that he could clearly see the underside of the wing. The tow plane then crossed the projected runway centerline from north to south and passed below the trees at the end of the runway and out of his view.

Another witness, who lived in a house south of runway 7 and adjacent to the tow plane landing zone, was pulling out of her driveway westward when she immediately observed an airplane fly directly in front of her from right to left. Familiar with the airport traffic, she assumed it was abandoning the landing approach and joining the left downwind traffic pattern for runway 25. However, the airplane then descended below a set of power lines and appeared to turn right. It then initiated a rapid climb, rolled inverted, rolled back over, and struck the ground nose down.

The tow plane was subsequently located in a dirt field 900 ft southwest of the threshold of the gravel portion of runway 7.

Pilot Information

Certificate: Airline transport 
Age: 67, Male
Airplane Rating(s): Single-engine land; Single-engine sea; Multi-engine land
Seat Occupied: Single
Other Aircraft Rating(s): Glider; Helicopter Restraint Used: 5-point Instrument Rating(s): Helicopter
Second Pilot Present: No
Instructor Rating(s): Helicopter 
Toxicology Performed: Yes
Medical Certification: Class 2 With waivers/limitations 
Last FAA Medical Exam: August 21, 2015
Occupational Pilot: UNK
Last Flight Review or Equivalent:
Flight Time: (Estimated) 13500 hours (Total, all aircraft), 90.8 hours (Total, this make and model) The pilot, age 67, had an extensive career in military and civilian aviation, including experience as an experimental test pilot, which he gained while attending the Naval Test Pilot School.

He held an airline transport pilot certificate with ratings for airplane multiengine land and commercial privileges for airplane single-engine land, single-engine sea, rotorcraft-helicopter, instrument helicopter, and glider. He also held a flight instructor certificate for rotorcraft-helicopter and type ratings in the North American 265 Sabreliner (T-39) and Aérospatiale SA 330 Puma.

He reported 13,500 total flight hours at his last Federal Aviation Administration (FAA) airman medical examination 6 days before the accident. Documentation provided by SCSA indicated that, during the period from July 8, 2013, through June 8, 2015, he had accumulated 90.8 total flight hours in the PA-25, including 424 tows.

Aircraft and Owner/Operator Information

Aircraft Make: Piper
Registration: N4369Y
Model/Series: PA 25 260 
Aircraft Category: Airplane
Year of Manufacture: 1969
Amateur Built: No
Airworthiness Certificate: Restricted (Special)
Serial Number: 25-4872
Landing Gear Type: 
Tailwheel Seats: 1
Date/Type of Last Inspection: September 7, 2014 Annual 
Certified Max Gross Wt.: 2899 lbs
Time Since Last Inspection: 20 Hrs
Engines: 1 Reciprocating
Airframe Total Time: 11789 Hrs as of last inspection
Engine Manufacturer: LYCOMING
ELT: Not installed
Engine Model/Series: O-540 SERIES
Registered Owner:
Rated Power: 260 Horsepower
Operating Certificate(s) Held: None

The single-seat, tailwheel-equipped airplane was manufactured in 1969 and had accrued 11,789 total flight hours as of its last annual inspection on September 7, 2014. It was equipped with a six-cylinder Lycoming O-540-G1A5 engine, serial number RL-25988-40E, that was
manufactured in January 2013.

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual (VMC) 
Condition of Light: Day
Observation Facility, Elevation: KPMD,2582 ft msl
Distance from Accident Site: 15 Nautical Miles
Observation Time: 18:53 Local 
Direction from Accident Site: 306°
Lowest Cloud Condition: Clear
Visibility 10 miles
Lowest Ceiling: None
Visibility (RVR):
Wind Speed/Gusts: 5 knots /
Turbulence Type Forecast/Actual:  /
Wind Direction: 340° 
Turbulence Severity Forecast/Actual:  /
Altimeter Setting: 30.1 inches Hg
Temperature/Dew Point: 34°C / 3°C
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: Llano, CA (46CN)
Type of Flight Plan Filed: None
Destination: Llano, CA (46CN)
Type of Clearance: None
Departure Time: 11:50 Local 
Type of Airspace: Class E

At 1153, the automated surface weather facility at Palmdale USAF Plant 42 Airport, Palmdale, California, elevation 2,543 ft mean sea level (877 ft below, and 15 miles northwest of, the accident site) reported wind from 340° at 5 knots, 10 miles visibility, temperature at 94° F, dew point 37° F, and an altimeter setting at 30.10 inches of Mercury. The temperature rose to 97° F 1 hour later.

Immediately following the accident, the SCSA General Manager checked the weather and recorded a temperature of 94° F with a 4-knot wind out of the west.

Airport Information

Airport: CRYSTAL 46CN 
Runway Surface Type: Dirt; Gravel
Airport Elevation: 3420 ft msl
Runway Surface Condition: Dry
Runway Used: 07R
IFR Approach: None
Runway Length/Width: 1000 ft / 32 ft 
VFR Approach/Landing: Traffic pattern

Wreckage and Impact Information

Crew Injuries: 1 Fatal
Aircraft Damage: Substantial
Passenger Injuries:
Aircraft Fire: None
Ground Injuries: N/A 
Aircraft Explosion: None
Total Injuries: 1 Fatal
Latitude, Longitude: 34.483055,-117.83583

The cabin sustained crush damage from the firewall to the forward legs of the pilot's seat. The remaining aft fuselage structure and the empennage section sustained minimal damage. Both wings remained attached to the fuselage by their respective main spars and lift struts. The left wing leading edge had twisted upward, and the wing sustained crush damage in an aft direction throughout its entire length. The right wing exhibited leading edge crush damage outboard of the lift strut attachment points.

The engine remained partially attached to its mount and had shifted downward and right of the fuselage centerline. One propeller blade exhibited a forward 5° bend midspan, and the second blade sustained chordwise scratches along its entire surface and nicks to its leading edge. The fuel tank bladder was exposed, had been breached, and came to rest covering the engine. Although no fuel was found in the tank, the soil under the engine was soaked with a liquid that smelled like aviation gasoline.

Additional Information

The pilot had driven up from his home in San Diego the night before the accident and had slept on the foldout bed in the SCSA clubhouse that night. A club member observed him watching a football game there late in the afternoon, but by sunset, the lights were out.

According to SCSA's club members, the fuel truck typically contains bottles of water, which are given to the tow pilot during refueling. An empty bottle of water was found in the wreckage at the accident site.

Medical and Pathological Information

The Department of the Medical Examiner-Coroner, County of Los Angeles, performed an autopsy on the pilot, and the cause of death was determined to be "multiple blunt force injuries."

In addition, hypertrophic heart disease was identified with the heart weighing 530 grams. The heart was described as "somewhat globular," and the myocardium as "mildly floppy." The right ventricle was 0.5 centimeter (cm), the interventricular septum was 1.5 cm, and the left ventricle was 1.7 cm thick. No significant coronary artery stenosis was identified, and the remainder of the cardiac examination was unremarkable.

According to records obtained from the pilot's personal physician, the pilot had longstanding high blood pressure that was treated with lisinopril. In 2013, he had volunteered to be a van driver for the US Department of Veterans Affairs, which required that he have a cardiac evaluation. During the evaluation, the initial stress test was stopped after 6 minutes 25 seconds due to shortness of breath and "S-T depression" in the lateral leads. A follow-up stress test with nuclear imaging was subsequently performed, and no anomalies were detected. The pilot's wife reported that, about 1 year before the accident, the pilot had experienced a 10- to 15-minute episode of unusual dizziness and an "odd" feeling while hiking on a hot day.

During his most recent FAA medical examination, the pilot reported having high blood pressure controlled with medication and previous surgeries. At that time, he reported that he used lisinopril and minocycline and that he was 71 inches tall and weighed 238 lbs. He was subsequently issued a second class medical certificate with the limitation that he wear corrective lenses. He did not report heart or vascular trouble at the time of the application.

Lisinopril is a blood pressure lowering medication available by prescription and is commonly sold with the trade names Prinivil and Zestril. Minocycline is an antibiotic often used to treat or prevent acne. 

The FAA Civil Aerospace Medical Institute performed toxicological tests on specimens from the pilot. The results were negative for carbon monoxide and all screened drug substances and ingested alcohol. (Refer to the toxicology report included in the public docket for specific test parameters and results.)

All available medical data were reviewed by a National Transportation Safety Board (NTSB) Medical Officer, who concurred that the autopsy's results were consistent with a diagnosis of hypertrophic cardiomyopathy, or a diffuse enlargement and thickening of the heart.

Tests and Research

Security Camera Footage

Portions of the day's tow operations were captured on two security video cameras located on the roof at the west end of the airport administration building, 1,500 ft west-northwest of the runway 7 threshold. Both cameras were directed down and toward the building's parking lot, and both cameras had a horizontal field of view of about 70° with the camera on the north side of the building (camera 5) facing west and the second camera in the center of the building (camera 4) facing west-southwest. The camera's field of view overlapped; however, the images recorded by camera 4 were blurred and out of focus.

Camera 5 captured distant images of the initial climb sequences of tow flights one, two, three, four, and six and the base and final landing approach legs for tow flights one and six. During the two captured landing approaches, the tow plane performed a sweeping and fluid transition from a right downwind to final approach, which took about 30 seconds. On both occasions, the tow plane was silhouetted against the sky, and it both entered and departed from the top left sector of the camera's field of view.

For the accident landing approach, the tow plane entered the camera's field of view in the top left sector, but this time, it was about half the altitude of the previous flight, such that it was silhouetted against the foothills. It travelled from left to right and overshot the runway centerline, at which point it appeared to initiate a climbing right turn to the northeast and then departed the camera's field of view to the right. Seven seconds later, the tow plane came back into view travelling south from right to left while in a right bank of about 60°. The wings appeared to rock as the airplane crossed back over the runway centerline and out of the top left field of the camera's view.

Camera 4 captured the last 9 seconds of the flight after it crossed the centerline, and although the image was blurred, the airplane appeared to initiate either a climb or left turn before disappearing from view. About 1 second later, a plume of dust appeared from the ground near the wreckage.

An approximation of the terrain features in reference to the camera locations revealed that, during the approach, the tow plane overshot the runway centerline by ¼ mile to the north. It then returned, overshot the runway centerline a second time, and subsequently collided with the ground about 600 ft south of the centerline.

In an effort to calculate the tow plane's flightpath relative to the standard traffic pattern, a series of flight tests were performed using SCSA's second PA-25 tow plane. During the tests, a pilot completed multiple takeoffs and landings to and from runway 7 while both cameras 4 and 5 were recording. Review of the footage revealed that, while flying the standard pattern and altitudes, the airplane was above camera 5's field of view for most of the approach, becoming briefly visible at the top center for about 5 seconds as it transitioned from the base leg to final approach. No images of the tow plane were captured by camera 4. The on-board GPS track data for the tow plane revealed that it was descending from about 500 ft above ground level (agl) for the period it was in view of, and approaching, camera 5. SCSA standard operating procedures require a minimum clearance of 200 ft agl over the power lines at the approach end of runway 7. These lines are immediately adjacent to both cameras.

Engine and Airframe Examination

Postaccident examination of the airframe and engine did not reveal any anomalies. A complete report is contained in the public docket.

The airplane was equipped with a JPI EDM-700 engine data monitor, which recorded exhaust gas and cylinder head temperatures (EGT, CHT) for all cylinders and battery voltage. The unit was sent to the NTSB Office of Research and Engineering for data extraction. The extracted data indicated similar trends in CHT and EGT for all of the flights on the day of the accident, including the accident flight, with CHT rising to an average of about 360° F during each 12-minute cycle. EGT remained about 1,150° F for the initial 9 minutes, rising to about 1,400 for 2 minutes, before returning to 900° as the cycle resumed.

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