N7MCDehavilland DHC-6-100 · 1967

On April 19, 2016, about 2115 central daylight time, a Beech 65-A90-1 airplane, N7MC, collided with towers suspending high-power transmission lines while attempting to land at Slidell Municipal Airport (ASD), Slidell, Louisiana. Both pilots were fatally injured, and the airplane was destroyed. The airplane was registered to and operated by the Saint Tammany Parish Mosquito Abatement District as a 14 Code of Federal Regulations Part 91 public aircraft operations flight . Night visual meteorological conditions existed at the airport at the time of the accident, and the flight was operating on a visual flight rules flight plan. The local flight originated about 2000.

After completing a planned mosquito abatement application flight, the pilots radioed their intention to land at ASD. The accident pilots were flying a visual pattern to runway 18, and another company airplane was behind them conducting a practice GPS approach to runway 18. When the pilot of the other company airplane radioed that they had crossed the GPS approach's final approach fix, the accident pilot radioed that they were on the left base leg and were number one to land at the airport. Seconds later, the pilots of the other company airplane saw a blue arc of electricity, followed shortly after by a plume of fire. The accident pilots could not be reached on the radio, and the company pilots notified emergency personnel. The airplane was located in a marsh about 0.6 nautical mile north-northwest of the approach end of runway 18.

Pilot

The left seat pilot, age 59, held a commercial pilot certificate with ratings for airplane single-engine land, airplane multiengine land, and instrument airplane. In addition, he held a flight instructor certificate for airplane single-engine and instrument airplane. He was issued a second-class medical certificate, dated February 18, 2016, with the limitation that he must wear corrective lenses for near and distant vision. On his medical application, the pilot reported that he used hydrochlorothiazide and irbesartan.

As of December 11, 2015, the pilot reported accruing 6,825 hours of single-engine total time with 50 hours logged in the preceding 6 months and 952 hours of multiengine total time with 15 hours logged in the preceding year. His flight time in the Beech C90 was 15 hours with 5 hours logged in the preceding year. He estimated that he had 7,762 total hours with 1,135 hours of night time, 10 hours of actual instrument time, and 305 hours of simulated instrument time. He reported his last biennial flight review occurred in February 2014.

Company records showed that the pilot flew the accident airplane for 7.4 hours in 2015 and 5.7 hours in 2014. On July 1, 2015, the pilot was approved by the aerial operations supervisor to act as pilot-in-command for the accident airplane and a Britten-Norman BN-2T airplane, N717MC.

Copilot

The copilot, age 68, who was in the right seat, held an airline transport pilot certificate with ratings in airplane single-engine land, multiengine land, rotorcraft-helicopter, and instrument airplane and helicopter. He also held a commercial pilot certificate for airplane single-engine sea and a flight instructor certificate for airplane single and multiengine, rotorcraft-helicopter, and instrument airplane and helicopter. He was issued a second-class medical certificate, dated July 14, 2015, with the limitation that he must have available glasses for near vision. On his medical application, the copilot reported that he used diltiazem, losartan, pravastatin, metoprolol, etodolac, pantoprazole, sildenafil, and warfarin.

As of February 25, 2016, the pilot reported accruing 4,310 hours of single-engine total time with 50 hours logged in the preceding 6 months and 5,910 hours of multiengine time with 105 hours logged in the preceding year. His flight time in the Beech C90 was 627 hours with 59 hours logged in the preceding year. He estimated that he had 18,163 total hours with 4,619 hours of night time, 2,199 hours of actual instrument time, and 431 hours of simulated instrument time. He reported that his last biennial flight review occurred in February 2014.

The copilot was also the department's aerial operations supervisor. He had worked for the Saint Tammany Parish Mosquito Abatement District for 31 years. According to other company pilots, although the copilot was the more senior pilot, he was seated in the right seat and would have been performing copilot duties.

Both pilots had flown the accident airplane together on April 4, 7, 8, 11, and 18, 2015, for a total of 6.9 hours. Each flight ended in a night landing to ASD. On the forms for each of the flights, the area for "comments and/or mechanical problems" was blank.

The low-wing, twin engine airplane was manufactured in 1968. It was powered by two 550-shaft- horsepower Pratt & Whitney Canada PT6A-20 turboprop engines. Each engine drove a three-blade, variable-pitch, full-feathering Hartzell HC-B3TN-3B propeller. The airplane was operated as a public aircraft operations flight by the Saint Tammany Parish of Louisiana for mosquito abatement purposes.

The airplane's most recent inspection was a combined Phase I through IV and annual inspection recorded on December 1, 2015, at an airframe total time of 15,189.6 hours. On that date, the left engine had accrued 9,676.6 hours since new and 1,638.4 hours since overhaul. The right engine had accrued 7,413 total hours since new and 1,248.5 hours since overhaul. Airplane forms filled out before the flight showed that the airplane had logged 15,207.1 total hours.

The airplane was originally manufactured as a US Army U-21D. It remained in military service until 1995 when it was sold to a civilian company. In 1998, the airplane was registered with the Federal Aviation Administration (FAA) as a Beechcraft 65A90-1 and issued a special airworthiness certificate for restricted use for the purpose of agriculture and pest control. The airplane was acquired by the Saint Tammany Parish in June 2012. The airplane was equipped with a radar altimeter and had controls installed in both pilot seats.

At 2053, the ASD automated weather reporting facility reported calm wind, visibility 10 miles, clear sky, temperature 68° F, dew point 64° F, and a barometric pressure of 30.09 inches of mercury .

Astronomical data from the US Navy Observatory indicated that the moon rose on the day of the accident at 1730 and set the following morning at 0541. The moon disk illumination was 94%.

The low-wing, twin engine airplane was manufactured in 1968. It was powered by two 550-shaft- horsepower Pratt & Whitney Canada PT6A-20 turboprop engines. Each engine drove a three-blade, variable-pitch, full-feathering Hartzell HC-B3TN-3B propeller. The airplane was operated as a public aircraft operations flight by the Saint Tammany Parish of Louisiana for mosquito abatement purposes.

The airplane's most recent inspection was a combined Phase I through IV and annual inspection recorded on December 1, 2015, at an airframe total time of 15,189.6 hours. On that date, the left engine had accrued 9,676.6 hours since new and 1,638.4 hours since overhaul. The right engine had accrued 7,413 total hours since new and 1,248.5 hours since overhaul. Airplane forms filled out before the flight showed that the airplane had logged 15,207.1 total hours.

The airplane was originally manufactured as a US Army U-21D. It remained in military service until 1995 when it was sold to a civilian company. In 1998, the airplane was registered with the Federal Aviation Administration (FAA) as a Beechcraft 65A90-1 and issued a special airworthiness certificate for restricted use for the purpose of agriculture and pest control. The airplane was acquired by the Saint Tammany Parish in June 2012. The airplane was equipped with a radar altimeter and had controls installed in both pilot seats.

The airplane initially impacted two 70- to 80-ft-tall towers that suspended high-power transmission lines . The lines generally ran on a heading of 150°/330° and, due to their height, were not required to be illuminated. Ceramic isolators were shattered on the northern pole, and the top guide wire was damaged on the southern pole. A portion of the airplane's lower chemical tank and left wing tip were found directly beneath the poles. The airplane's debris path followed a 175° heading in marshy terrain for about 555 ft.

The main wreckage came to rest about 0.6 nautical mile northwest of runway 18's approach end. The main wreckage consisted of the metal hopper tank frame, the upper portion of the fuselage, cockpit instrumentation, inboard left wing, outboard right wing, left horizontal, vertical stabilizer, rudder, and the left engine with its propeller. A postimpact fire consumed a majority of the cabin structure. The airplane's nose was generally aligned with 350° magnetic, and the fuselage was inverted.

Flight control continuity was confirmed to all surfaces. The flaps were in the retracted position. The elevator and rudder trim positions could not be determined due to impact damage. The fuel selector position could not be determined. The emergency locator transmitter (ELT) was still attached to the airplane, and the antenna and was found in the "armed" position, but it was thermally damaged. The company pilots in the other airplane reported that they did not hear any ELT beacon.

Both pilots' restraint hardware remained latched; the webbing was consumed by fire. The left fuel flow gauge read 400 pounds per hour and the right fuel gauge read 250 pounds per hour. The cockpit instrumentation was impact and thermally damaged and was largely unreadable. The right inlet turbine temperature gauge read about 700°. The left propeller speed read about 1,100 rpm.

The right engine was impact-separated and found upright. Its propeller remained attached to the engine. Two of the three blades displayed S-bending with nicks on their leading edges. Examination of the left propeller blades found one blade almost completely consumed by the postcrash fire. Another blade was partially consumed and displayed curling with a rearward bend. The third blade was curled and bent rearward. No anomalies were detected with the airframe and engine.

A thermally damaged SD card was recovered from the airplane's ADAPCO Wingman GX system and sent to the National Transportation Safety Board laboratory for data extraction. Due to the damage sustained in the accident, the chips on the card were not recoverable.

The FAA's Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A), dated 2008, Chapter 10, "Night Operations," states the following:

Night Illusions

A black-hole approach occurs when the landing is made from over water or non-lighted terrain where the runway lights are the only source of light. Without peripheral visual cues to help, pilots will have trouble orientating themselves relative to Earth. The runway can seem out of position (downsloping or upsloping) and in the worse case, results in landing short of the runway. If an electronic glide slope or visual approach slope indicator (VASI) is available, it should be used. If navigation aids (NAVAIDs) are unavailable, careful attention should be given to using the flight instruments to assist in maintaining orientation and a normal approach. If at any time the pilot is unsure of his or her position or attitude, a go-around should be executed.

Approaches and Landings

To fly a traffic pattern of proper size and direction, the runway threshold and runway-edge lights must be positively identified. Once the airport lights are seen, these lights should be kept in sight throughout the approach. Distance may be deceptive at night due to limited lighting conditions. A lack of intervening references on the ground and the inability of the pilot to compare the size and location of different ground objects cause this. This also applies to the estimation of altitude and speed. Consequently, more dependence must be placed on flight instruments, particularly the altimeter and the airspeed indicator.

The altimeter and VSI [vertical speed indicator] should be constantly cross-checked against the airplane's position along the base leg and final approach. A visual approach slope indicator (VASI) is an indispensable aid in establishing and maintaining a proper glidepath.

The accident pilots were communicating on the airport's common traffic advisory radio frequency (CTAF), which was not recorded. The pilots in the company airplane who were also on the CTAF reported no distress calls before the accident.

Pilot

The St. Tammany Parish Coroner's Office conducted an autopsy on the pilot. The autopsy showed no natural diseases that could have posed a potential hazard to flight safety.

The FAA Civil Aerospace Medical Institute performed forensic toxicology on specimens from the pilot. Testing was negative for carbon monoxide and ethanol. The following drugs were detected:

Ibuprofen detected in urine

Irbesartan detected in urine

Irbesartan detected in blood

The pilot had previously reported the use of irbesartan, which is used to treat high blood pressure, to the FAA. Ibuprofen is a nonnarcotic analgesic and anti-inflammatory agent and is available in prescription and nonprescription forms.

Copilot

The St. Tammany Parish Coroner's Office conducted an autopsy on the copilot. Although the autopsy did note several chronic medical conditions, there did not appear to be any natural diseases that posed an immediate hazard to flight safety.

The FAA Civil Aerospace Medical Institute performed forensic toxicology on specimens from the copilot. Testing was negative for ethanol and 15% carbon monoxide was detected in blood from the heart. The following drugs were detected:

Diltiazem detected in urine

Diltiazem detected in blood (heart)

Metoprolol detected in urine

Metoprolol NOT detected in blood (heart)

Rosuvastatin detected in urine

Rosuvastatin detected in blood (heart)

Warfarin detected in urine

Warfarin detected in blood (heart)

The copilot had previously reported all of the detected medications except the rosuvastatin to the FAA. Rosuvastatin is a prescription medication used to reduce blood cholesterol and triglycerides levels.