Thursday, May 25, 2017

Grumman G-164A N6894Q, Heimgartner Aviation LLC: Accident occurred March 11, 2016 in Juliaetta, Latah County, Idaho

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

Additional Participating Entity:
Federal Aviation Administration / Flight Standards District Office; Spokane, Washington

Aviation Accident Final Report - National Transportation Safety Board: https://app.ntsb.gov/pdf

Investigation Docket - National Transportation Safety Board: https://dms.ntsb.gov/pubdms

Aviation Accident Data Summary - National Transportation Safety Board: https://app.ntsb.gov/pdf

Heimgartner Aviation LLC: http://registry.faa.gov/N6894Q

NTSB Identification: WPR16LA082 
14 CFR Part 137: Agricultural
Accident occurred Friday, March 11, 2016 in Juliaetta, ID
Probable Cause Approval Date: 05/23/2017
Aircraft: GRUMMAN G164, registration: N6894Q
Injuries: 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The commercial pilot was conducting an agricultural application flight. The pilot reported that, while maneuvering the airplane about 300 ft above ground level, the engine experienced a partial loss of power. Unable to maintain altitude, the pilot conducted an emergency landing to a field, during which the airplane landed hard and nosed over, coming to rest inverted. Postaccident examination of the engine revealed that the No. 2 cylinder head exhibited a circumferential crack of its barrel between the cooling fins.

The Federal Aviation Administration had previously issued an airworthiness directive (AD) to address cylinder head cracking on the accident model engine. The AD required periodic visual inspections for cracks in the cylinder heads at specified intervals of time in service (every 100 hours for the accident airplane). According to the engine maintenance logbooks, the AD was last complied with about 35 hours before the accident. The previous inspections to this were sporadic, indicating that neither maintenance personnel nor the owner(s) were regularly complying with the AD.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
A partial loss of engine power due to a crack in the No. 2 cylinder. 

HISTORY OF FLIGHT

On March 11, 2016, about 1725 Pacific standard time, an Grumman G-164A, N6894Q, experienced a partial loss of power and collided with terrain during an off airport landing in Juliaetta, Idaho. Heimgartner Aviation LLC., was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 137. The commercial pilot, the sole occupant, was not injured; the airplane sustained substantial damage. The local aerial application flight departed from a private road in Juliaetta about 1720. Visual meteorological conditions prevailed and the pilot did not file a visual flight rules (VFR) flight plan.

The pilot stated that the purpose of the flight was to apply 1,600 pounds of (dry) fertilizer to wheat fields. He had completed around 20 loads earlier in the day which equated to about 4 hours of flight time. The airplane departed with a half-full fuel tank and climbed to about 500 feet above ground level (agl). After configuring the airplane to the appropriate manifold pressure and turning the carburetor heat on, the pilot maneuvered the airplane toward the field he intended to spray. While in level flight, about 300 feet agl, the engine began to violently shudder and make loud backfiring noises. The engine experienced a partial loss of power. The airplane continued to descend, unable to maintain level altitude. The airplane landed hard and nosed over, coming to rest inverted.

AIRPLANE INFORMATION

The airplane, a Grumman G-164A, serial number 1730, was equipped with a Pratt and Whitney R985-AN14B engine, serial number P225620. The operator provided excerpts from the engine logbooks that included the AD lists and the last maintenance performed. The records indicated that the last annual inspection was recorded as being completed in April 2015 at a tachometer time of 5,402 hours; the tachometer time at the time of the accident was 5,435, or about 35 hours after the maintenance.

In May 1978 the Federal Aviation Administration (FAA) issued an Airworthiness Directive (AD) 78-08-07 applicable to Pratt & Whitney R-985 series engines. The AD required periodic visual inspections for cracks in the cylinder heads at specified intervals of time in service. According to the AD, visual inspections of the cylinder heads are required at intervals not to exceed 100 or 150 hours of time in service, depending on whether the they have been ultrasonically inspected. 

The logbook excerpts contained a document listing AD 78-08-07, which showed that the most recent compliances occurred in April 2007 and April 2015 (during which time about 1,970 flight hours accrued). The entirety of the AD list only showed 78-08-07 as being complied with in May 2001. On that list, the only AD that showed compliance thereafter was in April 2015 for the cylinder hold-down nuts as per AD 56-06-02.

TESTS AND RESEARCH

A post accident examination revealed that cylinder no. 2 was cracked around almost the entire circumference of the barrel in between cooling fins.

The carburetor, part number 391598, was examined at Precision Engines. The bench test revealed no anomalies that would have precluded normal operation. Upon disassembly investigators found no debris in the main metering nozzle, float needle seat, idle metering tube, and accelerator pump; no debris was noted in the metering jets.

ADDITIONAL INFORMATION

According to the NTSB aviation accident database, after AD 78-08-07 became effective there were a total of 3 accidents involving Pratt and Whitney R-985 engines that had a cylinder failure.

A similar query was conducted of the FAA's Service Difficulty Report (SDR) database. Among the results, 34 of the reports documented a cylinder crack or separation as the cause of the service difficulty.

According to a representative at Covington Aircraft Engines, an aircraft engine maintenance, repair and overhaul facility that specializes in R-985 engines, they seen many cracks in cylinders. He stated that the reasons for the cracks are predominantly twofold: the carburetor is worn, resulting in the engine running too lean (creating hotspots in the cylinder); and thermal fatigue cracks from the pilot shock cooling the engine (an excessively rapid descent going from a high temperature differences within the metal and not the absolute temperature of the metal).

The Transport Canada Civil Aviation issued a Service Difficulty Advisory No. AV-2007-2 regarding R-985 cylinder heads. In pertinent part it stated, "It is very important that operators properly warm-up and cool-down the engine before and after flight. This will significantly minimize distress to the engine. It is essential that the cylinder assembly be adequately warmed up in order to "heat stretch" the cold cylinder, especially before applying high power. Failure to do so can lead to fatigue cracks and cause distress to the cylinder head and other rotating parts of the engine. Problems associated with cylinder head separation and cylinder barrel flange cracks can be minimized if attention to cylinder head temperature limitations is closely followed."

NTSB Identification: WPR16LA082 
14 CFR Part 137: Agricultural
Accident occurred Friday, March 11, 2016 in Juliaetta, ID
Aircraft: GRUMMAN G164, registration: N6894Q
Injuries: 1 Uninjured.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed. NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

On March 11, 2016, about 1725 Pacific standard time, a Grumman G-164A, N6894Q, experienced a partial loss of power and collided with terrain during an off airport landing in Juliaetta, Idaho. Heimgartner Aviation LLC., was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 137. The commercial pilot, the sole occupant, was not injured; the airplane sustained substantial damage. The local aerial application flight departed from a private road in Juliaetta about 1720. Visual meteorological conditions prevailed and the pilot did not file a visual flight rules (VFR) flight plan.

The pilot stated that the purpose of the flight was to apply 1,600 pounds of fertilizer to wheat fields. He had completed around 20 loads earlier in the day which equated to about 4 hours of flight time. The airplane departed with a half-full fuel tank and climbed to about 500 feet above ground level (agl). After configuring the airplane to the appropriate manifold pressure and turning the carburetor heat on, the pilot maneuvered the airplane toward the field he intended to spray. While in level flight, about 300 feet agl, the engine began to violently shudder and make loud backfiring noises. The engine experienced a partial loss of power, and the airplane was unable to maintain altitude. During the off airport forced landing, the airplane landed hard and nosed over, coming to rest inverted.

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