Flight Details
Aircraft Type: Dornier Do-228-202 Operator: Sita Air Registration: 9N-AIE Flight Number: ST916 Route: Tenzing-Hillary Airport (LUA), Lukla to Ramechhap Airport (RHP), Nepal Date of Incident: 16 April 2025 Total Occupants: 17 (passengers and crew) Weather Conditions: Visual meteorological conditions enroute; no reported turbulence or adverse weather
Introduction
On 16 April 2025, a Sita Air Dornier 228 operating flight ST916 from Lukla to Ramechhap experienced an in-flight hydraulic failure at approximately 12,000 feet altitude while southeast of Kathmandu. The crew elected to divert to Tribhuvan International Airport (KTM), where the aircraft landed safely on runway 02. Following landing, the aircraft required towing to the apron due to loss of hydraulic power affecting steering or braking capability. All 17 occupants remained unharmed, and the aircraft returned to service roughly 20 hours after the event. The incident is categorised as an inflight systems malfunction involving the hydraulic subsystem.
Sequence of Events
The flight departed Lukla’s high-altitude airfield as part of a routine shuttle to Ramechhap, a route commonly used during trekking seasons for connections to and from Mount Everest region trails. Approximately halfway into the flight, while cruising at 12,000 feet and about 50 nautical miles southeast of Kathmandu, the flight crew detected a hydraulic system fault.
Upon confirmation of the hydraulic issue, the crew initiated a diversion to Kathmandu — the nearest airport with extended runway facilities, firefighting services, and mechanical support. There was no reported loss of control or instability in flight, and the aircraft remained under full manual control throughout the descent.
Sita Air coordinated with Kathmandu ATC, and priority handling was granted. The Dornier 228 landed safely on runway 02 without additional complications. However, due to the hydraulic issue, the aircraft lacked full steering and braking capability and required towing from the runway exit to the terminal apron.
Crew & Communication
The two-person flight crew operated in accordance with emergency protocols and standard operating procedures (SOPs) for hydraulic system failure on the Do-228. Communications with Kathmandu Approach and Tower were timely and clear. The flight did not declare a Mayday but did request expedited handling to facilitate systems checks and secure landing.
Upon touchdown, the crew managed a controlled rollout, keeping the aircraft aligned on centreline until it could safely decelerate and come to a halt. Ground services were pre-briefed and towed the aircraft to the stand for inspection. No other aircraft operations at Kathmandu were significantly delayed by the event.
Aircraft Systems & Technical Analysis
The Dornier 228 is a twin-turboprop STOL (Short Takeoff and Landing) aircraft equipped with a basic hydraulic system supporting limited functions — primarily brakes, nosewheel steering, and flap operation. The failure of this system can result in:
Loss of hydraulic-assisted braking Limited or no nosewheel steering Retraction/extension issues with trailing edge flaps
In this incident, no abnormal flight control issues were reported, suggesting the hydraulic loss was isolated to non-primary systems.
Post-flight technical inspection would have focused on:
Hydraulic fluid levels and system integrity Hydraulic pump (engine-driven or electric) performance Accumulator pressure and return line condition Potential leaks in flap actuators, brake lines, or steering servo valves
The aircraft was returned to service within 20 hours of the event, indicating the issue was resolved either by component replacement, seal repair, or system repressurisation.
Passenger Experience & Cabin Conditions
Passengers onboard did not experience any inflight disturbance or major symptoms of failure. Cabin pressure and environmental systems remained unaffected. Given the routine appearance of the descent and landing, most passengers were unaware of the technical issue until after disembarkation.
There was no cabin announcement of an emergency, though the flight crew may have briefed the cabin crew discreetly regarding the situation. No medical attention or passenger support services were required post-landing.
Emergency Response & Aftermath
Tribhuvan International Airport’s ground crews were pre-alerted and positioned alongside runway 02 during the landing. ARFF services stood by but were not required to intervene. Once the aircraft came to a stop, a tug and tow bar were dispatched to relocate the aircraft to a secure maintenance position.
Airport operations continued without significant disruption. Sita Air coordinated passenger transfer and onward travel where applicable, although no diversion from the original passenger destination of Ramechhap was reported beyond the aircraft itself.
Investigation Status
Nepal’s Civil Aviation Authority (CAAN) was notified of the occurrence and classified it as a non-serious incident. Sita Air initiated an internal technical review and submitted a maintenance report to regulators.
The investigation is focused on determining the precise cause of the hydraulic failure. Common root causes in similar incidents include:
Undetected hydraulic fluid leak Failure of hydraulic pump motor Malfunctioning pressure relief valve Internal failure of actuating components
No safety directive or fleet-wide implications have been reported so far.
Root Cause & Contributing Factors
While the final technical report is pending, preliminary conclusions indicate a mechanical or fluid-related failure in the Dornier 228’s hydraulic circuit. Given the aircraft’s prompt return to service, the failure was likely:
Isolated to a minor component or seal Non-catastrophic in nature Contained to secondary systems with no compromise to airworthiness
The crew’s timely detection and conservative diversion prevented escalation.
Contributing operational factors may include:
Lack of enroute maintenance diversion options between Lukla and Ramechhap Terrain constraints requiring decisive rerouting in case of systems issues Limited redundancy in light aircraft hydraulic architecture compared to modern jetliners
Safety Recommendations & Industry Impact
While the incident does not warrant broad systemic changes, Sita Air and other operators of the Dornier 228 may consider:
Enhanced hydraulic pre-flight checks during mountain operation seasons Review of fluid level monitoring and trend analysis during short-haul sectors Procedural emphasis on early decision-making in system fault scenarios
For airports like Lukla and Ramechhap with minimal diversion infrastructure, aircraft operating these routes should maintain conservative safety margins for system performance and alternate planning.
Conclusion
The diversion of Sita Air flight ST916 to Kathmandu following a hydraulic failure enroute from Lukla reflects sound crew judgment and standard systems handling. Despite the technical fault, the aircraft landed safely, and no injuries or damage were reported. Prompt engineering intervention led to a same-day return to service.
The event highlights the need for vigilance in system monitoring, especially in aircraft operating in remote or rugged environments with limited diversion flexibility.
Disclaimer
This article is based on publicly available information and reports at the time of writing. While every effort has been made to ensure accuracy, we cannot guarantee the completeness of the information provided.
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