Surviving Helicopter Ditching

Every year, when the South West Monsoon hits India, a niggling question faces naval and offshore helicopter crew who must fly against strong winds, leaping waves and blinding rain to undertake missions or reach their offshore destinations.

What if I have to ditch the helicopter?

European Aviation Safety Agency (EASA) defines ditching as “an emergency landing on water, deliberately executed in accordance with rotorcraft flight manual (RFM) procedures, with the intent of abandoning the rotorcraft as soon as practicable.”

NH90 crash at sea Jul 19, 2020. Netherlands MoD photo (via Vertical Magazine)

Case 1: Recently, two officers from Dutch Navy died after their NH-90 helicopter “came down in the Caribbean Sea near Aruba on Sunday (19 July 2020) at the end of a coast guard patrol”. Two other crew members escaped without major injury. A photo (above) shows the wreckage of the helicopter floating upside down with the Emergency Flotation System (EFS) inflated. An investigation is underway. At this point, it is not clear if it was a ‘crash’ or ‘ditching’ (both have potentially different implications for survivability).

Case 2: On 29 Apr 2017, crew of an AW 139 (Regn A6-AWN) ex-Abu Dhabi Aviation ditched at sea seven minutes after takeoff from Dhabi II oil rig for another rig BUNDUQ. “Because the oil temperature continued to increase, the Commander decided to descend to 200 ft in preparation for a possible ditching. While descending through 210 ft, and with an oil temperature of 119°C, the flight crew heard a loud grinding noise emanating from the gearbox area. The Commander followed the instruction in the QRH and decided to ditch the Aircraft“, the report reads.

Photo of AW 139 (Regn A6-AWN) ex-Abu Dhabi Aviation ditched at sea 29 Apr 2017

Photos of the ditched helicopter shows it floating perfectly, but upside down. Two flight crew members and one passenger managed to escape with their lifejackets into a life raft before the helicopter capsized due ‘slow deflation’ of the left-aft float. The crew had activated the emergency floats (EFS) prior touchdown on water.

The AW139 can carry 15 passengers in high-density seating configuration. A6-AWN had just one passenger in the cabin when they ditched (aircraft took-off from Abu Dhabi with five pax; four disembarked at Dhabi II rig). The particular model of AW 139 had two liferafts packed into sponsons on either side that could be deployed by activating handles in the cockpit. Only one life raft deployed; more than sufficient for three survivors. The flight deck had a sum total of 32,000 hours flying experience. Weather or sea state was hardly a factor, with mild winds of 7 to 8 kts and visibility in excess of 7 kms.

This paragraph from the accident report is important:

The Investigation identified that the causes of the deflation were a tear of the bag fabric and seam delamination. It was identified that the in-flight activation of the flotation bags was not compliant with the certification of the Aircraft’s flotation system, which caused the deployed float cover to fragment. The remains of the float cover probably caused a tear to the aft left flotation bag. The Investigation also identified that many flotation bags did not pass inflation tests during regular shop visits because of seam problems.”

High intensity naval and offshore flying goes on unabated under the belief that EFS “guarantees” safe ditching upto “sea state 6” (or whatever the type-specific RFM specifies). But ask ‘how to determine sea state’ and crew shrug their shoulders with a tentative answer: “from prevailing winds?”. There are no weathermen or oceanographers in Bombay High. Often, weather app Windy or the ship / rig’s anemometer (with unknown position errors) are the only tools.

Wind speed is a ‘necessary but not sufficient’ condition to determine sea state. Wave height depends both on local and remote winds (swell). Oceanographers utilise terms such as ‘fetch‘ (horizontal distance over which wave-generating winds blow) and ‘duration’ of prevailing winds to determine sea state. Both ‘fetch’ and ‘duration’ of the blow are required to develop a particular sea state. There is definite correlation between wind speed and sea state. But this is subject to oceanographic parameters, without which a direct correlation can be incorrect or misleading.

There is Beaufort Scale for winds and a WMO Code Table 3700 for sea state (SS). There are some grey areas of overlap. Can these scales be used interchangeably for offshore flying? For instance, Beaufort Scale 6 means “strong breeze” of 22-27 knots, “where large waves begin to form; the white foam crests are more extensive everywhere; probably some spray”. Sea state 6 describes the sea as “very rough” with a wave height of 4-6 metres. These are two different scales.

As per EASA, sea state is “a classification of sea conditions established by the World Meteorological Organization (WMO)“. Interestingly, the WMO itself no longer recommends the use of sea state. It has been replaced by ‘significant wave height’ (Hs). Indian offshore crew can at best expect to receive wind speed from an offshore destination. This is extrapolated to sea state and life goes on, sometimes straddling a difficult space between letter and spirit. Flying continues as per ‘reported winds’ and not ‘significant wave height’; one is ‘objective’ while other is ‘subjective’. There are no suitable alternatives available presently.

The Flight Crew Operating Manual (FCOM) of AW 139 (Section 1, Supplement 9) states: “the Emergency Flotation and Life Raft System is approved for ditching, up to Sea State 6, in accordance with JAR/FAR 29“. The next paragraph lays down a number of conditions, including provision of approved equipments such as life rafts, number of passengers (basis life raft capacity), life preservers, emergency locator transmitter (ELT), etc.

AW 139s operating offshore keep EFS (floats) “armed” throughout the flight between crossing coast outbound/inbound. In the ditching report of Abu Dhabi Aviation AW139, the captain’s decision to operate the EFS prior touchdown in water was questioned. The Bell 412 RFM on the other hand carries a specific “WARNING” prohibiting operation of floats in forward flight:

SEVERE NOSE UP PITCHING WILL OCCUR IF EMERGENCY FLOATS ARE INFLATED IN FORWARD FLIGHT OR DESCENT. — from Bell 412 EP RFM

If EFS is destabilising in flight, who has seen its behaviour after meeting a “very rough” sea?

Aeroplanes have well-rounded, buoyant fuselage, huge wings and tail planes (remember Sully and his “Miracle on the Hudson”?). In contrast, the helicopter is short, stubby and, at best, bears the flotation characteristics of a boulder falling off a cliff (see this video). Some helicopters such as the Westland Sea King were specifically designed with a ‘boat hull’; with watertight integrity and buoyancy. We have also seen US Marine Corps Chinooks “floating” with engine power in placid waters as special forces drove into their cargo hold in powered rafts.

But all this is without EFS inflation. Once inflated, EFS can be draggy and destabilising, especially if ditching with forward speed. With EFS inflated, takeoff is “prohibited” for most helicopters. Some helicopters like the Bell 412 are specifically designed with ‘high-skid’ configuration to accommodate EFS. Offshore helicopters in general operate with EFS, push-out windows for the cabin, life-preservers and emergency breathing system (EBS) for pax, thereby ensuring maximum survivability in the event of ditching.

A Bell 412 with emergency floats deployed for tests

Case 3: In a memorable accident from naval archives (Feb 1, 1981), young Lt Cdr Subodh Purohit (later Cmde, RiP) and his crew from Indian Navy undertook a copybook ditching of Sea King 503 at sea after a main rotor malfunction during an oceanic passage. The helicopter with four occupants floated on EFS for almost seven hours while help arrived. The helicopter later capsized after taking in water even as the crew were rescued by a lifeboat. “The marvelous job as Captain of the aircraft carried out by ‘Subbo’ while floating – his continuous commentary reminding us that Seakings can float for 8-10 hrs; naval ships would have sailed to reach us in the next 7-8 hrs, and so on, to keep our morale high. Last but not the least, the timely decision to descend from 8500 ft to 200 ft made all the difference between life and death“, Cmde Rajendra Sharma, TACCO on that flight, recounted in a story he wrote 38 years later. This was a Sea King, a ‘flying frigate’, with boat-shaped hull designed for ‘single-engine water takeoff’ after ditching.

A Seaking 42B in ASW hover (Picture courtesy Indian Navy)

Today, most helicopter EFS are designed for auto-inflation on water impact. Compact, high-speed, multirole helicopter designs derived from ‘landlubber’ cousins have all but abandoned the ‘boat hull’ concept. For the military, a high level of training and preparedness for ditching can be assumed. Can this be taken for granted in civil aviation where 15 passengers (read “clients”) are often sandwiched between ‘devil and the North Sea’ in high-density seating configuration of, say, an AW139, with no consideration for the sea state below? Food for thought.

The purpose of EFS is to provide adequate time and stability for crew and passengers to escape a ditched helicopter. A 2016 Notice for Proposed Amendment (NPA) from EASA states:

“In an otherwise survivable water impact, most fatalities occurred as a result of drowning because the occupants were unable either to rapidly escape from a capsized and flooded cabin, or to survive in the sea for sufficient time until rescue. Furthermore, the testing environment in which helicopters are type-certified for ditching bears little resemblance to the sea conditions experienced in operation.” (Italics for emphasis mine)

The last line is a clincher & perhaps formed basis for the EASA NPA that aimed to fill these gaps.

JAR 29.801 lays down the specifications for ditching and EFS. Sub-para (b) requires that “each practicable design measure, compatible with the general characteristics of the rotorcraft, must be taken to minimize the probability that in an emergency landing on water, the behavior of the rotorcraft would cause immediate injury to the occupants or would make it impossible for them to escape“.

Understandably, actual ditching trials would be too dangerous and impractical. Hence, sub-para (c) of JAR 29.801 that “the probable behavior of the rotorcraft in a water landing must be investigated by model tests or by comparison with rotorcraft of similar configuration for which the ditching characteristics are known. Scoops, flaps, projections, and any other factors likely to affect the hydrodynamic characteristics of the rotorcraft must be considered“.

How many of us (naval, offshore crew & certification agencies) have read these lines with the seriousness it deserves?

Certification requirements for ditching are often met through modelling, simulation and “read-across”. When the helicopter arrives on surface of water, metacentric height will face-off with Centre of Gravity (CG). Simulation and modelling can only go so far. Such trials also don’t factor intangibles like human anxiety, panic, disorientation, etc.

In Indian waters, we are fortunate to have sea surface temperatures that may not induce shock or hypothermia. For the navy, extrapolating this to inclement weather, or far reaches of operational deployment seen in recent times, could pose new challenges.

Offshore crew may also like to consider cultural aspects specific to country. Many of us in Indian offshore have seen highly obese passengers asserting their ‘window seat’ rights in high-density seating configuration just to maximise their own survival in the unlikely event of a ditching. Extrapolate this to ditching in ‘Sea State 6’ and we have some serious concerns. Even the North Sea operators and UK CAA grappled with harsh realities of ditching survivability that ultimately resulted in CAP 1145.

Is equipping rotorcraft with EFS a “necessary & sufficient” condition for safe ditching? Is lack of EFS an obituary to the helicopter or its occupants? Do we take certification and approvals for ditching at face value or is there a need to balance this against contextual and cultural reality of our operations? History informs us that behaviour of aircraft, weight & balance, correct deployment of EFS, use of ‘air pockets’ or EBS, and, most importantly, training and readiness of crew and passengers will ultimately determine the outcome of a ditching.

Simply ticking boxes won’t help!


Kaypius will get you more on this topic in a follow-on article. Please stay tuned. Meanwhile, I welcome your valuable feedback, experiences and thoughts for future designs in the comments box below or at kipsake1@gmail.com.

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©KP Sanjeev Kumar, 2020. All rights reserved. I can be reached at kipsake1@gmail.com or on my Twitter handle @realkaypius. Views are personal. Cover photo courtesy Indian Navy.

 

5 thoughts on “Surviving Helicopter Ditching

  1. Very well written. Had witnessed live rescue of Cmde S Purohit & other Seaking crew from warship where I was a Mid.

  2. Sir, thanks to this article, I’ve started seeing merit in IN’s request for purpose built naval helicopters as opposed to navalised AF ones.
    Having a boat shaped airframe shall be helpful as possibilities of immediate rescue are remote due to paucity of air assets. But doing that would entail re-designing the entire aircraft.
    Even IN’s insistence on twin engined platforms with capability to take off on one seems reasonable.
    Solution might lay in getting naval helicopter designed by joint team of HAL & DND using available components like engine, avionics etc.
    That brings us to subject of cost. Having a dedicated fabrication unit for order of 100 odd helicopters is bound to make them very expensive.
    Costs cannot be reduced without maximum utilisation of use of helicopters in India & HAL cornering substantial share of civil market with flying equivalent of Maruti.
    All this seems unachievable & so strengthens case for preference of imported platforms over local ones.
    Is my interpretation correct or is it way off the mark?

  3. As usual KPS touches upon a relevant topic for Helicopter operations, both Military as well as Commercial. My two pence worth…

    1. All machines give adequate warning before pulling the proverbial rug from under the feet of the crew. It is for the operator and the crew to keep a sharp look out for any signs of failure. Low and slow is the name of the game if you suspect something, because impact on water from height or with fwd speed or both are bound to be catastrophic.

    2. A timely decision for a controlled ditching may save the day and chances of survivability. A crash resulting from pushing your luck is unlikely to leave survivors.

    3. The boat shaped hull is a wonderful concept for flying over the sea, and one wonders why it has failed to extend to modern design of off shore helicopters. The considerations must be economics accruing from mass production. The EFS is a poor cousin of the boat shaped hull and the fact that certification is resulting from simulation on models says a lot about their likely effectiveness.

    4. As KPS brings out once in contact with water the Metacentric height will clash with the CG and the photos of most ditching show the obvious winner is the CG. It is to Cmde Purohit’s credit that he was able to ditch his aircraft successfully and ensure safety of his crew. An unusual case where the Metacentric height played off successfully against CG.

    5. The key to survivability then is to train crew and pax for egress from inverted aircraft because that’s the most likely scenario in the event of a crash and ditching in rough sea states.

    6. The real battle for the crew will begin on successful egress of a ditched aircraft because their survivability depends on availability of long range SAR and SAR crew confidence at extended ranges.

    7. One learns something new every day and am grateful to KPS for enlightening on the concepts of ” fetch” and “blow” and wave height with regard to Sea State.

    8. Bottom line is the crew must ensure well maintained aircraft when flying over water cause the medium is quite unforgiving. In the commercial world with revenues plunging south its anybody’s guess about the pressures faced by the off shore industry and its Helicopter crew.

    Safe flying and Happy Landings

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