The S-61L had an enlarged cabin and dispensed with some of the amphibious features, such as its float stabilizers, for greater payload capacity.

However, operations in this sector proved troublesome, with profits elusive and service often subject to noise complaints and accidents.

In September 1957, Sikorsky was awarded a United States Navy development contract for an amphibious anti-submarine warfare (ASW) helicopter capable of both detecting and attacking submarines.

The initial production aircraft being powered by a pair of General Electric T58-GE-8B turboshaft engines, each capable of providing up to 1,250 shp (930 kW).

[5] On 2 November 1961, the S-61L conducted its maiden flight; it was 4 ft 3 in (1.30 m) longer than the HSS-2 to facilitate the carriage of a substantial payload of freight or passengers.

Both the S-61L and S-61N were subsequently updated to the Mk II standard, which was outfitted with more powerful CT58-140 engines that provided superior performance in hot and high conditions, along with incorporating measures to dampen vibration and various other refinements.

This model includes composite main rotor blades, a modular wiring harness, and (optionally) a glass cockpit; these changes reportedly boost the helicopter's lift capability as well as increase its speed.

[3] While regarded as one of the most successful American scheduled helicopter airlines even by the 21st century, following several accidents involving its S-61s, including the crash of the prototype S-61 N300Y, Los Angeles Airways ceased operations in 1971.

[13] Launched on 21 December 1965, the operation soon proved to be unprofitable, only carrying an average of only eight passengers, leading to the heliport's closure in 1968.

While flights were resumed during February 1977, an accident three months later involving a S-61 helicopter that collapsed and flipped onto its side, killing five people, led to the heliport being closed indefinitely.

20 towns and cities covered by the network, including Bogra, Sirajganj, Chittagong, Mongla, Kushtia, Barisal, Chandpur, Sandwip and Hatiya Upazila.

[16] While the operation proved valuable prior to the opening of the M25 motorway, its noise led to it being a point of controversy, the route overflying several densely populated areas of London.

Initially, the Civil Aviation Authority banned flights between 9:15 pm and 6:30 am to limit its impact, but the whole service came to an end after its licence to operate was revoked by the Transport Secretary on 6 February 1986.