Published on April 13th, 2017 | by Mark Dwyer0
Preliminary Report Published into Rescue 116 Accident
The Air Accident Investigation Unit (AAIU) have published the Preliminary Report into the accident of Rescue 116, EI-ICR at Black Rock Co. Mayo on 14th March. The Coast Guard Helicopter, a Sikorsky S-92A, disappeared while on approach to Blacksod Lighthouse during a top cover mission in the early hours of the morning. The AAIU have published a 39 page preliminary report, which indicates the complexity and enormity of the task of investigating this accident. The details of the mission and the identity of the crew involved have been well publicised so this article will focus on the facts as laid out in the preliminary report.
The report centres on the avionics installed in the cockpit of the S-92A and the information presented to the flight crew. In particular, three systems are looked at in detail, the Radio Altimeter, Automatic Flight Control Systems (AFCS) and the Enhanced Ground Proximity Warning System (EGPWS).
The helicopter is fitted with two Rad Alts, each Rad Alt interfaces with two antennas which are fitted to the bottom of the helicopter and provides the height of the helicopter above the surface whenever it is within 2,500 ft of the surface. The RA is one of the inputs to the AFCS.
The AFCS includes eight SAR modes, which are controlled from either Mode Select Panel. There are four SAR approach modes, three hover modes and one departure mode. In each approach mode, the helicopter transitions from a high speed, high altitude condition to a low speed, low altitude condition. The approaches attempt to follow programmed deceleration and descent schedules, with decreasing airspeeds corresponding to decreasing radio altitudes.
The EGPWS is designed to decrease instances of Controlled Flight Into Terrain (CFIT) by increasing pilot situational awareness. The EGPWS uses two sets of modes to protect against CFIT. Both sets provide visual and aural alerts when terrain/obstacle clearance is not assured. The basic modes (Modes 2 through 6) are based on RA. The basic modes prevent descent into level or evenly sloping terrain. The enhanced or ‘look ahead’ modes are based on GPS position compared to terrain and obstacle databases. The look ahead modes are intended to prevent the aircraft from running into sharply rising terrain or man-made obstacles. The EGPWS also provides a digital terrain map that allows the pilot to view a representation of terrain and obstacles ahead, provided these are contained in the databases.
In relation to Black Rock and its Lighthouse the EGPWS manufacturer informed the Investigation that;
“The lighthouse obstacle is not in the obstacle database and the terrain of the island is not in our terrain database.” Honeywell explained to the Investigation that: “Honeywell’s DO-200A compliant processes include the integration and validation of multiple data sources, both authoritative (Government and Type 1 LOA suppliers) and non-authoritative (public and private data). Typical terrain data sources include remote sensor data (e.g., SRTM, ASTER) as well as topographical map digitized data. Obstacle data sources include Government AIP data, supplied by our Type 1 LOA supplier, as well as non-authoritative data furnished by customers, governments and private industry. Honeywell’s selected terrain and obstacle source data do not include Black Rock.”
“Honeywell’s terrain data is sourced from our supplier [named supplier]. It is a digitized topographic map derived data set. It does not include Black Rock. We have looked at alternate sources, including SRTM and ASTER. While Black Rock is present in these alternate data sets, the actual altitude of Black Rock is considerably higher than what is indicated in these alternate data sets. Our obstacle data for the Ireland region is sourced from our Type 1 LOA supplier, [named supplier]. This data is originated by the [named source], and does not include obstacles on Black Rock.”
The Investigation is continuing to engage with Honeywell and other parties/agencies to reach a full understanding of this issue.
Low Altitude Switch
To allow for helicopter operations that require low altitude flight, an EGPWS ‘Low Altitude’ function can be enabled with a switch. This function is designed for flight at low altitude in VFR conditions. When this function is engaged:
- Mode 1 is inhibited
- Mode 2 warning boundaries are significantly reduced
- Mode 3 warnings are inhibited above 100 ft AGL
- Mode 4 warning boundaries are significantly reduced
- Mode 6 “ALTITUDE, ALTITUDE” callout is enabled
- Terrain Advisory look ahead distances are reduced
CVR data indicates that the Low Altitude Switch was engaged at the time of the accident.
An initial review of the available data from the CVR, FDR, HUMS, AIS, ATC and marine radios communications has established the following factual information:
- The Commander for the mission was seated in the right hand side cockpit seat and was the pilot flying. The other pilot, seated in the left hand side cockpit seat, was also a qualified helicopter commander; he was the Co-pilot (Pilot Monitoring) for the flight.
- The CVR indicates that crew communications were mission-focused and considered, with minimal extraneous conversation.
- The helicopter initially routed towards Sligo on departure from Dublin. Following the completion of inflight fuel and time calculations, the destination was changed to Blacksod Lighthouse for an uplift of fuel prior to a planned routing towards the location of the SAR mission being conducted by R118.
- The initial cruise altitude for the flight was 3,000 ft AMSL . En route the helicopter climbed to 4,000 ft AMSL before crossing mountainous terrain in Co. Mayo.
- The Crew made extensive attempts to establish two-way radio communications with R118. Two-way communications were briefly established on secure VHF radio, whilst R118 was in the vicinity of Blacksod for refuelling.
- The Commander programmed the “APBSS (Blacksod South) Route” into the FMS during the cruise and the Co-pilot confirmed that the route matched the Operator’s Route Guide.
- The Commander briefed the Crew on the plan for arrival at Blacksod Lighthouse.
- The CVR recorded the Commander commenting to the other Crew Members on a number of occasions that it had been a substantial period of time since she had previously landed in Blacksod. On one occasion the Commander asked the Co-pilot when he had last been into Blacksod and he indicated that he had not been there recently.
- The helicopter commenced a descent from its cruising altitude (4,000 ft) when abeam the waypoint BKSDA en-route to the waypoint BLKMO.
- The undercarriage was extended and three green lights were indicated during the descent.
- The helicopter descended initially to 2,400 ft, whereupon the Commander selected the APP1 mode to establish the helicopter at 200 ft AMSL and 80 kts. Thereafter, the airspeed was manually adjusted to 75 kts due to the Commander’s stated expectation of tailwinds on the easterly leg of the arrival.
- The Commander’s stated intent was to complete the APP1 procedure prior to turning east towards waypoint BLKMO to commence the arrival route to Blacksod Lighthouse.
- The Commander set the Rad Alt to 180 ft and the auto-hover height to 150 ft.
- The Primus 701 Weather Radar was set to the GMAP2 Ground Mapping Mode; the system manufacturer’s manual indicates that this mode provides the best sensitivity for ground mapping of targets. This mode disables all ground clutter and sea clutter reduction modes (*CR1 and *CR2 modes)
- A weather radar range of 10 miles was requested by the Commander and the Copilot confirmed this selection.
- The CVR recording contains no reference by the Crew to the presence of a lighthouse or terrain at Black Rock during their briefing for APBSS.
- The LOW ALT switch on the EGPWS was confirmed as ON by the Commander and cross-checked by the Co-pilot.
- The Commander had the moving map displayed on her MFD and the Co-pilot had weather radar displayed on his MFD.
- The CVR recordings indicated that the Co-pilot was using the weather radar to identify terrain features.
- The Rad Alt provided a callout of “ALTITUDE, ALTITUDE” 26 seconds prior to the initial impact. The Commander identified the reason for the aural alert as a small island below the helicopter which she said was “just a small little island… that’s B L M O itself”. At the time of the aural alert FDR data placed the Helicopter in the vicinity of an outcrop of two rocks, Carrickduff and Carrickad, which are located approximately 0.65 nm to the west of the Black Rock.
- A rear crew member identified an island, probably through the use of the EO/IR camera, approximately 13 seconds prior to the initial impact with terrain. He said “looking at an island just in, directly ahead of us now guys, you want to come right [Commander’s Name]”.
- In response to a query “OK, come right just confirm?” from the Commander, the rear crew member said “twenty degrees right yeah”, and a heading change was initiated using heading mode. The rear crew member then interjected, with increasing urgency, “Come right now come right COME RIGHT”.
- The helicopter rapidly pitched nose up during the two seconds prior to the initial impact.
- Following the initial impact, the data indicates that the helicopter climbed while experiencing large changes in pitch, roll and yaw angles.
- Within two seconds after the initial impact, the three green lights indicating that the undercarriage was down and locked stopped illuminating and the ‘TOO LOW GEAR’ aural alert was triggered.
Following the accident, debris from the helicopter was found on Black Rock, floating in the sea to the east of the rock and washed up on the shoreline of counties Mayo and Donegal. The main wreckage was found by locating the acoustic beacon attached to the MPFR; it was located in 40 m of water off the southeast side of Black Rock.
The report makes 2 interim Safety Recommendations;
- CHC Ireland should review/re-evaluate all route guides in use by its SAR helicopters in Ireland, with a view to enhancing the information provided on obstacle heights and positions, terrain clearance, vertical profile, the positions of waypoints in relation to obstacles and EGPWS database terrain and obstacle limitations.
- RFD Beaufort Ltd should review the viability of the installation provisions and instructions for locator beacons on Mk 44 lifejackets and if necessary amend or update these provisions and instructions taking into consideration the beacon manufacturer’s recommendations for effective operation.
The full Preliminary report can be read HERE.