Helicopter Pilots Synchronize Their Altitude with Ship Heave to Minimize Energy When Landing on a Ship’s Deck

ABSTRACT

Objective: This study aims at investigating helicopter pilots’ strategies to achieve ship deck landing.

Background: Helicopter maritime operations are challenging, especially when it comes to landing on the moving decks of small ships, such as frigates, which can lead to dramatic accidents.

Method: Expert pilots were requested to fly the full ship landing maneuver from approach to touchdown in an immersive simulator. Two sea states (3 and 4 on the Douglas Sea scale) and their resulting deck movements were used. Changes in helicopter altitude were correlated with deck heave movements throughout the maneuvers in order to scrutinize the helicopter-deck coupling. The energy at impact was measured.

Results: The dynamics of helicopter-deck coupling evolved through two phases during the maneuver: Initially, no coupling then, coupling in phase between the helicopter vertical displacements and deck heave displacements. Moreover, the coupling reached higher values within the last 15 m to landing, corresponding to a hover phase and touchdown, and the correlation increased with sea level. This coupling might help in improving pilots’ safety since the greater the coupling at touchdown, the lesser the kinetic energy at impact.

Conclusion: Coupling the helicopter vertical displacements with ship heave movements seems to be an efficient strategy to minimize energy at impact. Questions arise on both the rationale and the perceptual invariant behind such behavior and indicate the necessity of further investigation.

Acknowledgments

The authors wish to thank David Wood (English at your Service, http://www.eays.eu/) for revising the English of the manuscript. The participation of Mathieu Thomas in this research project was supported by a grant from the Direction Générale de l’Armement (DGA) and the Office National d’Etudes et de Recherches Aérospatiales (ONERA).

Disclosure Statement

No potential conflict of interest was reported by the authors.

Supplementary Material

Supplemental data for this article can be accessed on the publisher’s website.

Notes

1. “In seakeeping terminology, the Quiescent Period is known as the period of calm in rough waters to allow the ship to perform operations such as landing aircraft and unmanned aerial vehicles (UAVs), as well as the entry of landing craft in the basin. Quiescence refers to the interval of time where all ship motions are within acceptable limits to perform a desired activity” (Riola et al., 2013).

2. The astern procedure consists of approaching the ship’s deck from the stern along the ship’s center line until reaching the hover position over about 10–15 ft above the flight deck before performing a vertical descent to land. This procedure is usually adopted world-wide for precautionary or emergency landings, given that the helicopter is already in the right profile for emergency procedures.

3. The fore-aft procedure consists of approaching the ship’s deck from the stern, along a line to the left or right of the ship’s centreline (called fore-aft port or fore-aft starboard procedures, respectively), approximately 1.5 times the diameter of the main rotor at the center of the deck. Then, the helicopter flies side-wards following the “bum-line” horizontal deck marking from the hover alongside right or left position to the hover over about 10–15 ft above the flight deck before performing a vertical descend to land. Since in most cases, the pilot flying is sitting in the right seat, the fore-aft port procedure enables the best visual cues with the ship (Hoencamp, 2015).

4. Good Energetic conditions imply a sufficient velocity at impact to stick on the deck, especially in the case of deck roll at touchdown but acceptable velocity at impact to avoid structural damages on the helicopter (US Navy, NATOPS Flight Manual, US Navy, 2004) and trauma on pilots’ spines (Desjardins et al., 1989).

Additional information

Funding

This work was supported by the Direction Générale de l'Armement (DGA); and the Office National d'Etudes et de Recherches Aérospatiales (ONERA).