The present flight deck lighting system onboard Royal Navy and Royal Fleet Auxiliary ships comprises a combination of floodlights to illuminate the deck and a fixed row of ‘horizon’ lights mounted athwart ships, usually on the aft face of the ship’s hangar. Although this system has worked reasonably up until now, the introduction of larger aircraft and a trend toward using a single pilot has demanded a completely fresh appraisal of the visual cues available to the pilot, in order that he may meet the extended operational targets for which the aircraft has been designed.

One criticism of a conventional deck lighting system is that it poorly defines the shape and ‘depth’ of the flight deck and, as the horizon lights are fixed, the pilot obtains no indication of the true horizon when flying at night or in poor visibility. In high sea states, when there is considerable roll motion, this can lead to spatial disorientation at a critical time of flying, i.e. that of final approach and landing onto a moving platform.

Two further disadvantages are that both of the present equipments use incandescent lamps which, not only are visually glaring to pilots, but are also incompatible with Night Vision equipment, the latter being increasingly used by Squadrons of the Royal Navy and other navies throughout the world.

Not withstanding these drawbacks imposed upon the pilot, the present system is also hazardous to the flight crew as the deck edge is not clearly defined. As a consequence of the above, the British Ministry of Defence contracted the Defence Research Agency to investigate alternative methods of providing visual guidance to helicopter pilots operating from naval ships. The proposed new suite of visual landing aids was fully trailed and tested, comprising a Stabilised Horizon Reference System (SHRS), matched to and linked with a pattern of Electro-luminescent Panels (ELP’S) used to define the outline of the ship’s flight deck, hangar screen, various sets of aircraft eye lines and other areas of the ship, to provide final positioning cues over the landing spot.

These trials demonstrated that helicopter operations could be safely extended outside of published night SHOLS and also resulted in a significant reduction of pilot workload. This system has been subsequently referred to as ‘Improved Approach Lighting’ or IAL, where the introduction of the ELP system is used to compliment traditional floodlighting. On 25 October 1996, the Ministry of Defence endorsed the requirement to fit ‘Improved Approach Lighting’ (IAL) to approximately 25 ships of the British Royal Navy and Royal Fleet Auxiliaries services. IAL has also been specified in the procurement specification for the Type 45 frigates.

In December 1996 Aeronautical & General Instruments Ltd were contracted by the Ministry to design and develop the IAL system in preparation for its introduction into RN service, a contract was placed only after the critical evaluation of alternative systems currently available on the market.

AGI’s Stabilised Horizon Reference System (SHRS) has been designed to compliment the Stabilised Glide Slope Indicator (SGSI) and flight deck lighting of LED or ELP design, to provide a total suite of visual landing aids. The system can be supplied with LED or advanced electro-luminescent (ELP) panels and comprises two fixed illuminated reference lights that are fitted to the ship’s main structure and a roll bar pivoted in the centre between the two fixed panels. The SHRS provides a ‘True Horizon’ reference to the pilot by utilising either the gyro signal to drive the bar in an equal and opposite direction to the ship’s roll motion. It has been designed to operate autonomously or in tandem with the AGI Stabilised Glide Slope Indicator and is fitted with an Automatic Parallel lock and audio/visual alarm in the event of fault detection.

View the System diagram of Stabilised Horizon Reference System