Cessna 402 N18VV accident near Boston, Massachusetts

Probable cause

The failure of a solid hydraulic fluid line, which resulted in a loss of hydraulic fluid that prevented the landing gear extension process from completing normally. Contributing to the outcome was the pilot’s failure to fully activate the emergency landing gear extension system.

NTSB analysis

The pilot reported that during climb out, he noticed a flicker of both the left and right hydraulic flow lights. He thought the airplane was losing hydraulic pressure, so he tried to extend the landing gear before all pressure was lost. Only the left main landing gear position green light illuminated. The hydraulic flow lights then illuminated steadily. He returned to the airport and performed the emergency landing gear extension checklist; however, the right and nose landing gear did not extend, and he landed with only the left main landing gear extended.

A postaccident examination of the airplane revealed that a solid hydraulic line connected to the hydraulic filter was fractured and the system contained no hydraulic fluid. It is likely that the fracture of the hydraulic line and the subsequent loss of hydraulic fluid resulted in the partial landing gear extension. A review of the airplane’s maintenance records could not determine the age of the hydraulic line or if any maintenance had been performed on the hydraulic line. Postaccident testing of the emergency landing gear extension system revealed that if functioned normally when the activation handle was fully extended. Based on this information, it is likely the pilot did not pull the emergency handle out far enough to activate the system.

Text from the NTSB. Open the NTSB docket for ERA24LA386 for the full record.