Engine & Emergency Flotation Failures – Greenland B206L4 Ditching

Posted by on Apr 21, 2025 in Accidents & Incidents, Crises / Emergency Response / SAR, Design & Certification, Helicopters, Maintenance / Continuing Airworthiness / CAMOs, Offshore, Safety Management, Survivability / Ditching | 0 comments

Engine & Emergency Flotation Failures – Greenland B206L4 Ditching (Sermeq Helicopters OY-HIO)

On 28 February 2024 Bell 206L4 OY-HIO Sermeq Helicopters ditched in Tunulliarfik Fjord (the inner section of Skovfjord) near Qaqortoq in southern Greenland.  Although the Emergency Flotation System (EFS) was activated, it malfunctioned and the helicopter rolled over.  The pilot, the sole occupant, escaped unharmed.

Wreckage of Sermeq Helicopters Bell 206L4 OY-HIO after Ditching in Tunulliarfik Fjord, Greenland (Credit: AIB)

Greenland is an autonomous territory within the Kingdom of Denmark and so the Accident Investigation Board (AIB) Denmark (Danish: Havarikommissionen for Civil Luftfart og Jernbane or HCLJ) investigated this accident.  They released their safety investigation report on 5 March 2025.

The Accident Flight

Th helicopter was making a VFR positioning flight from Narsarsuaq (BGBW) to Qaqortoq (BGJH) cruising at 1500 ft when…

…the engine chip detector light illuminated on the caution and warning panel, and a few seconds later, the engine low oil pressure light started illuminating.

Engine oil pressure indicated zero and indicated oil temperature decreased.  Moments after:

The N1 (Gas Producer Turbine rotations per minute) indication was zero, and both the engine-out warning light and horn activated.

However, the engine still produced power with a normal N2 (Power Turbine rotations per minute) indication.

Consequently the pilot selected a narrow sand bar alongside the steep southern cliffs of the fjord and initiated a powered descent.   

The engine however stopped and the pilot was forced to complete an autorotation, activating the EFS.  The helicopter ditched a few meters from the sand bar.  While the rotors were still turning the helicopter started slowly rolling onto its left hand side in a water depth of approximately 0.5 m. 

Wreckage of Sermeq Helicopters Bell 206L4 OY-HIO after Ditching in Tunulliarfik Fjord, Greenland (Credit: AIB)

The helicopter’s fixed Emergency Locator Transmitter (ELT) was mounted just below the instrument panel and fortuitously remained above the waterline.  It activated automatically, tiggering the tasking of a Search and Rescue (SAR) helicopter by Joint Arctic Command.

At 17:17 an Air Greenland H225 SAR helicopter arrived on scene and located the accident site at 17:29.  The pilot, who was wearing “ordinary clothing” and whose legs had gotten wet was found conscious but with a low body temperature, having sat outside in -5 °C for c75 minutes. He was kept in hospital overnight.

Safety Investigation – Survivability

The investigators note that the SAR operation was “effective and positively impacted the chance of survival in a hostile area”.

Though not legally required, in the opinion of the AIB, a survival suit in a hostile area would most likely have reduced the risk of hypothermia.

Safety Investigation – Engine

Following examination of the Rolls-Royce 250C30 engine the investigators concluded that the engine power loss was due to the following sequence of events:

The bearing no. 8 thrust plate anti-rotation tab separated from the thrust plate ring
and travelled with the engine oil to the scavenge side of the oil pump. 

The RR 250C30 no 8 bearing thrust plate from OY-HIO (right) and a new thrust plate with its braised tab intact (Credit: AIB)

Debris from the anti-rotation tab triggered the engine chip detector light.

Parts of the anti-rotation tab got trapped between a scavenge pump gear and the wall of the scavenge pump housing.

The oil pressure pump and scavenge pump stopped.

The drive shaft coupling from the fuel control gearshaft to the oil pump gearshaft fractured.

The Fractured RR 250C30 Oil Pump Drive Shaft Coupling (Credit: AIB)

There was no oil pressure and no N1 indication. The gas producer turbine and power turbine were still running.

A stopped scavenge pump resulted in no warm engine oil flowing from the engine to the airframe oil tank, where the engine oil temperature was measured. Hence the indicated temperature of the engine oil in the engine oil tank started to decrease.

Bearing no. 2, supporting the compressor impeller, started to degrade due to lack of lubrication caused by the stopped engine oil pressure pump.

Further degradation of bearing no. 2 led to a sudden hard contact between the impeller and the shroud. The impeller stopped turning, which led to the loss of engine power.

On 16 December 2022 Rolls-Royce had issued Commercial Engine Bulletin CEB-72-3309 introducing a new improved thrust plate.  This was manufactured in one piece instead of two pieces (a ring and anti-rotation tab) brazed together. 

This service bulletin had not been completed on the engine of OY-HIO.  AIB do not comment on whether the operator’s CAMO had assessed this CEB or what their conclusions were.

Safety Investigation – Emergency Flotation System (EFS)

The skid mounted Dart Aerospace Apical EFS consisted of 6 tri-bag floats.  A liferaft is integrated with the middle float on each side.

Example B206 with Apical EFS & External Liferafts (Credit: via AIB)

The investigators report that:

The float activation handle on the cyclic stick had been activated.  All floats apart from the LH aft float had been inflated.

Examination of the EFS found that:

All float gas supply lines and their connections from the gas reservoirs bottle to each float inlet valves were visually inspected without remarks, and all connections were [found] tightened.

Floats from OY-HIO. Aft float with inlet valves and interconnect hoses. Forward and mid floats only had two inlet valves (Credit: AIB)

Float and liferaft gas reservoir pressure gauges indicated zero pounds per square inch (psi), and the discharge valves were inspected without remarks.

The RH forward, mid, and aft float inlet valves and inlet valves interconnect hoses were inspected without remarks, and all connections were [found] tightened.

However:

The LH forward float inlet valves, including the interconnect hose, were inspected. The interconnect hose connection to the aft inlet valve were not properly tightened.

OY-HIO LH forward float interconnect hose connection to the aft inlet valve (Credit: AIB)

The connection was one-sixth (1/6) of a turn loose, and torque witness marks did not line up. Upon removal of the interconnect hose from the inlet valve, several drops of water came out.

There was salt debris in the aft inlet valve.

LH mid float inlet valves, including inlet valve interconnect hoses, were inspected without remarks, and all connections were tightened.

The LH aft float, uninflated, was inspected including its gas supply line hose, without remarks. However, the supply hose was not straight and had bends.

OY-HIO’s Kinked EFS Hoses (Credit: AIB)

The float was then serviced, reconnected and a test inflation was successful.

Test of OY-HIO’s Aft Float (Credit: AIB)

The liferaft release handle at the pedestal in the cockpit was partly pulled.

The external RH side liferaft release handle was fully pulled.

Two freezing tests of the complete float system were conducted…

…to determine how much water was needed in the supply hose to the LH aft float to prevent it from inflating when frozen.

For Test 1, 15 ml of water was injected into the LH aft float supply hose and kept the EFS in a chamber at -21 °C for 24 hours.  When tested all but the LH aft float, inflated.

EFS Test 1 (Credit: AIB)

For Test 2 only 7 ml of water was injected.  The forward chamber of the LH aft float did not inflate, because of icing of the forward inlet valve.

EFS Test 2 (Credit: AIB)

 

EFS Test: Icing of Valve (Credit: AIB)

Investigations revealed that:

During the latest required three-year inspection of the float system, the operator did not inflate the floats of the helicopter as required by the float manufacturer.

They concluded that:

Scheduled float inflation on the helicopter, as required by the float manufacturer, would likely have reduced the risk of (water) contamination in the supply lines to the floats.

However:

At the time of the accident, the float manufacturer’s “Instruction for Continued Airworthiness” document did not contain specific information on how to ensure float supply lines being clean and free of blockages/water.

They note that:

On the accident day, from start in the morning until the accident occurred, the helicopter operated in temperatures between -5° C and -10° C.

The supply line/hose to the LH aft float was not straight but had some light bends, allowing water to be trapped.

The investigators did not succeed in conclusively determining why water was present in the float supply lines, however:

…taking into consideration the combination of the actual operational outside air temperature and a lightly bended LH aft float supply line/hose, the AIB finds it likely that the LH aft float did not inflate due to frozen water being present in the supply line/hose to the LH aft float.

AIB Conclusions

En route, liberation of an anti-rotation tab from a thrust plate at engine bearing no. 8 resulted in a total engine power loss and, consequently, an autorotation over water.

Prior to ditching, the pilot activated the float system. However, the LH aft float did not inflate, resulting in the helicopter rolling over onto its left side upon ditching.

The likely reason for the LH aft float not inflating was frozen water in the supply line to the LH aft float.

Safety Actions

In October 2024, based on the investigation, the engine manufacturer issued a Revision 1 to the CEB-72-3309.  This replaced the original reason for the CEB…

…with one that had greater emphasis on the failure mode and potential consequences:

The compliance code was also upgraded from 5…

…to 3 with added emphasis:

The investigators also note that the float manufacturer will update their Instruction for Continued Airworthiness with instructions on how to verify that float supply lines are free of blockages/water before installation of the floats.

Safety Resources

The European Safety Promotion Network Rotorcraft (ESPN-R) has a helicopter safety discussion group on LinkedIn.  You may also find these Aerossurance articles of interest:

Aerossurance has extensive air safety, flight operations, SAR, airworthiness, human factors, helidecks, aviation regulation and safety analysis experience.  For practical aviation advice you can trust, contact us at: enquiries@aerossurance.com

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