Grumman G-164A accident near Monte Vista, Colorado, July 29, 2013
On July 29, 2013 at about 1:35 pm local time, a 1969 Grumman G-164A, registered N5324, was substantially damaged in an accident during enroute (cruise) near Monte Vista, Colorado. It was an aerial application (crop spraying) flight under agricultural flying rules (Part 137). No one was hurt; 1 person was on board or involved. The weather was visual conditions (good weather).
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The NTSB's probable cause their words, unchanged
The partial loss of engine power due to a fatigue failure of the engine cylinder exhaust rocker housing as a result of an excessively torqued rocker assembly.
Source: NTSB aviation accident database, copy made October 4, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 29, 2013 · about 1:35 pm local time
- Place
- Monte Vista, Colorado · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Grumman G-164A, built 1969 · all G-164As on the register
- Registration
- N5324 · registry record · serial 606
- Damage
- Substantial damage
- Flight
- Aerial application (crop spraying) flight · agricultural flying rules (Part 137)
The NTSB's narrative final · quoted from the NTSB record
The pilot reported that the aerial-application airplane experienced a partial loss of engine power while en route to the field to be sprayed. He jettisoned the airplane's chemical load following the loss of engine power, but the airplane was unable to maintain altitude and he made a forced landing in a pasture. During the forced landing, the right main landing gear separated from the fuselage after colliding with an irrigation ditch, and the airplane subsequently nosed over. A postaccident examination of the engine revealed a fatigue fracture of the No. 3 cylinder exhaust rocker housing. The measured release torque for the fractured No. 3 exhaust rocker assembly was at the upper limit of that specified by the manufacturer; however, the actual release torque before the failure was likely higher than when measured postaccident. Additionally, a majority of the other rocker assemblies had release torque measurements that exceeded the manufacturer's specified installation limits. Although the overhaul procedures used to assemble the rocker assemblies differed from the manufacturer's overhaul instructions, the investigation was unable to determine if those deviations would have resulted in excessive stress within the rocker housing. However, the investigation did conclude that the fatigue fracture was likely due to an excessive torque loading on the rocker assembly in conjunction with normal rocker operation. A definitive source of the over-torque condition could not be determined. The engine had accumulated 171 hours since being overhauled about 4 months before the accident. A review of the maintenance records found no history of unresolved airworthiness issues with the engine since the last overhaul. Additionally, the airplane owner and the primary maintainer of the airplane stated that no maintenance had been performed on any of the rocker assemblies since the last engine overhaul. A failure of the exhaust rocker housing would result in the corresponding exhaust valve remaining seated during engine operation. Without the typical pathway for the combustion products to be expelled through the engine exhaust, the hot gases would ignite the fuel/air mixture within the engine intake manifold. The likely result of a rocker housing failure would be an immediate and significant loss of engine power.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
What happened, in order
- Powerplant sys/comp malf/fail during enroute (cruise)
- Loss of engine power (partial) during enroute (cruise) defining event
- Off-field or emergency landing during landing
- Landing gear collapse during landing
- Nose over/nose down during landing
The NTSB's findings
- cause Aircraft › Aircraft power plant › Engine (reciprocating) › Recip eng cyl section › Fatigue/wear/corrosion
- cause Aircraft › Aircraft power plant › Engine (reciprocating) › Recip eng cyl section › Failure
Pilot
- Certificate: airline transport pilot, flight instructor
- Ratings: multi-engine land; single-engine land; single-engine sea; instructor: airplane single-engine; instructor: instrument airplane; instrument: airplane
- Flight time: 25,256 hours in all; 4,500 in this make and model; 180 in the last 90 days; 20,000 as pilot in command
- Last flight review: December 22, 2012
- Medical certificate: Class 2 (with waivers/limitations)
- Seat: sngl
- Injury: no injuries
The aircraft
- Airframe total time: 11,330.3 hours
- Last inspection: annual inspection, May 1, 2013; 171 hours since
- Maximum gross weight: 6,075 lb
- Seats: 1
- Landing gear: fixed
- Engine: Pratt & Whitney R1340 (piston); 10,296 hours total
- Operator: Crop Care Inc.
The flight
- Departed from: MVI Monte Vista CO at 1:30 pm
- Destination: MVI Monte Vista CO
- Flight plan: none
Weather at the time
- Light: daylight
- Wind: from 290° at 3 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 54°F (12°C), dew point 52°F (11°C)
- Altimeter: 30.26 inHg
- Observation at 1:52 pm from ALS, 12 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flig | 1 |
Other NTSB records under N5324 the same tail number, which may have belonged to a different aircraft at the time
About this page
Everything above comes from the NTSB's public accident database: the narrative, probable cause and findings are the NTSB's own words, and the coded tables behind its report (pilot, aircraft, flight, weather, injuries, sequence of events) are written out in plain English. Pilots' ages, home towns and medical details are left out on purpose. The docket at the NTSB holds the report as a PDF and the investigation's photographs and documents. This site never names pilots, passengers or anyone else involved. A preliminary report describes what is known soon after the event and can change; the final report, with the probable cause, usually follows one to two years later and this page is refreshed when it does. Case number CEN13LA443.