AAIB: Loss of control in flight led to Pawan Hans offshore crash in Sikorsky S

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The Indian Aircraft Accident Investigation Board (AAIB) has released the final investigation report into the Jun 28, 2022, offshore crash of a Sikorsky S-76D helicopter.

The board concluded the probable cause of the accident was, “uncontrolled flight during its final approach,” because of an undesired, aggressive nose-up maneuver, coupled with full lowering of the collective by the pilot flying.

This resulted in a steep autorotative descent at near zero speed, leading to impact with sea, investigators said.

Crew members’ lack of familiarization and proficiency with operating the helicopter’s automatic flight control system (AFCS) and failure to monitor the flight path at a critical juncture, have been cited as contributory factors among a host of active and passive failures at multiple levels in the organization.

The ill-fated helicopter VT-PWI — first of the S-76D to be inducted in Indian offshore operations — was being operated by Pawan Hans Limited (PHL) as part of a contract with India’s Oil and Natural Gas Commission (ONGC).

The helicopter took off with two pilots and seven passengers on a special visual flight rules (VFR) clearance from Juhu aerodrome at 05:35 UTC on Jun 28, 2022, for a crew change sortie to ONGC driller Sagar Kiran, jacked-up about 57 nautical miles off Mumbai. During final approach in inclement weather, the crew experienced a loss of control in flight (LOC-I) and crashed into the sea about 1.5 nautical miles from the rig.

Despite the high-energy impact with water (with a descent rate close to 2,000 feet per minute), all aboard managed to egress the helicopter that floated inverted on its emergency floatation gear (EFG).

Four passengers who made it out of the ditched helicopter drowned while five others (two crew plus three passengers) were recovered with injuries from the sea by search-and-rescue agencies. The board has pointed out glaring shortcomings in the rescue effort that likely contributed to the loss of lives.

The South West Monsoon was active over the Mumbai High offshore oilfield during that period, with seasonal rain and low visibility. The flight was uneventful from take-off till commencement of approach with the pilot-in-command (PIC) on controls as pilot flying (PF) for the outbound leg.

Offshore elevated deck approaches are omnidirectional, into wind, with the pilot who has the best view of the deck and obstructions acting as PF. Based on this assessment, controls were handed over by the PIC to the first officer about 1.5 nautical miles from the rig in an estimated visibility of about two miles.

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The first officer assumed the duties of PF while the PIC reverted to pilot monitoring (PM) at a crucial juncture when the rig and deck were perhaps not clearly visible.

Soon after handing over controls to the first officer, the PM went to “head down” mode to reach across the cockpit and put the weather radar to ‘standby’ from the co-pilot’s display.

The visual descent point (VDP) in a Category A approach to an offshore elevated deck is usually about one mile from the deck. It is a short, steep, continuously descending and decelerating approach that requires a clear view of the deck and the obstacle environment.

The AAIB found that the co-pilot (PF) acted on the cyclic trim release button and put the helicopter in a steep nose-up attitude with low collective setting soon after taking over. This went unmonitored by the PIC (PM) who was “head down” at that time.

Consequently, the helicopter entered a steep, autorotative descent with a low power setting, from which it could not recover. The PIC’s intervention, after enhanced ground proximity warning systems (EGPWS) issued “sink rate” and “pull up” alerts, proved too late and the helicopter impacted the sea in a high descent with right bank.

Discrepancies in the pre-flight passenger safety video briefing and self-briefing cards placed in the cabin led to confusion and incorrect operation of life preservers. This, combined with a rough sea and delay in rescue, sealed the fate of four passengers.

The fallibility of using trim release and appropriate use of automation in instrument meteorological conditions was covered in an earlier article for Vertical. Inappropriate or inadequate use of automation also contributed to the fatal crash of VT-PWA on Jan. 13, 2018, (LOC-I). In November 2015, another Airbus AS350 Dauphin N3 (VT-PWF) crashed during a night training flight off Mumbai High, killing both pilots (LOC-I). The last three fatal crashes in Mumbai offshore involved LOC-I on PHL helicopters flying for the ONGC.

The AAIB found no abnormality with the helicopter or its associated systems that could have contributed to the crash. The S-76D was inducted by PHL to meet the ONGC’s requirement for new helicopters as per their AS4 standards.

PHL pilots and engineers were trained in Sikorsky’s approved training organization and held valid licences.

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However, a series of delays and lapses in obtaining airworthiness approvals, the hiring of experienced expat pilots with valid foreign aircrew temporary authorization (FATA) and crew combination, led to PHL defaulting on “management of change,” safety management system and risk mitigation goals it had set for itself as defences against “severe” and “unacceptable” risks.

Two relatively experienced offshore pilots with low time on type (S-76D) were pushed into service during the inopportune window of the Southwest Monsoon.

Both PHL and ONGC are state-owned public sector undertakings. ONGC holds a 49 percent stake in PHL. ONGC workers unions refused to fly offshore in the S-76D soon after the accident, thus reverting to their dependency on PHL’s legacy Dauphin fleet, which the S-76D was meant to replace.