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The Sikorsky S-61L and S-61N are civil variants of the successful Sikorsky SH-3 Sea Kinghelicopter. They are two of the most widely used airliner and oil rig support helicopters built.
Design and development
In September 1957, Sikorsky won a United States Navy development contract for an amphibious anti-submarine warfare (ASW) helicopter capable of detecting and attacking submarines. The XHSS-2 Sea King prototype flew on 11 March 1959. Production deliveries of the HSS-2 (later designated SH-3A) began in September 1961, with the initial production aircraft being powered by two 930 kW (1250shp) General Electric T58-GE-8B turboshafts.
Sikorsky was quick to develop a commercial model of the Sea King. The S-61L first flew on 2 November 1961, and was 4 ft 3 in (1.30 m) longer than the HSS-2 in order to carry a substantial payload of freight or passengers. Initial production S-61Ls were powered by two 1350shp (1005 kW) GE CT58-110 turboshafts, the civil version of the T58. The S-61L features a modified landing gear without float stabilisers.
Los Angeles Airways was the first civil operator of the S-61, introducing them on 11 March 1962, for a purchased price of $650,000 each.
On 7 August 1962, the S-61N made its first flight. Otherwise identical to the S-61L, this version is optimized for overwater operations, particularly oil rig support, by retaining the SH-3's floats. Both the S-61L and S-61N were subsequently updated to Mk II standard with improvements including more powerful CT58-140 engines giving better hot and high performance, vibration damping and other detail refinements.
The Payloader, a stripped-down version optimized for aerial crane work, was the third civil model of the S-61. The Payloader features the fixed undercarriage of the S-61L, but with an empty weight almost 2,000 lb (910 kg) less than the standard S-61N.
Carson Helicopters was the first company to shorten a commercial S-61. The fuselage is shortened by 50 in (1.3 m) to increase single-engine performance and external payload.
A Coulson Aircrane S-61L dropping water during the Australia bushfire season.
A unique version is the S-61 Shortsky conversion of S-61Ls and S-61Ns by Helipro International. VIH Logging was the launch customer for the HeliPro Shortsky conversion, which first flew in February 1996.
One modification for the S-61 is the Carson Composite Main Rotor Blade. These blades replace the original Sikorsky metal blades, which are prone to fatigue, and permit a modified aircraft to carry an additional 2,000 lb (907 kg) load, fly 15 kn (28 km/h) faster and increase range 61 nmi (113 km).
The latest version is the modernized S-61T helicopter. The United States Department of State has signed a purchase agreement for up to 110 modernized S-61T aircraft for passenger and cargo transport missions in support of its worldwide operations. The first two modernized S-61 aircraft will support missions for the U.S. Embassy in Afghanistan.
Non-amphibious civil transport version. It can seat up to 30 passengers
S-61L Mk II
Improved version of the S-61L helicopter, equipped with cargo bins.
S-61 modernized upgrade by Sikorsky and Carson; Upgrades include composite main rotor blades, full airframe structural refurbishment, conversion of folding rotor head to non-folding, new modular wiring harness, and Cobham glass cockpit avionics; initial models converted were S-61N
N300Y, the Los Angeles Airways prototype of the Sikorsky S-61L Helicopter, lifting off from the Disneyland Heliport
On 2 February 1966 Flight 17, operated by a Sikorsky S-61 helicopter registration AP-AOC, crashed on a scheduled domestic flight in Faridpur Division, East Pakistan after the main gearbox failed, killing 23 of the 24 passengers and crew on board.
On 10 December 1966, operated by a Sikorsky S-61 helicopter registration AP-AOA, crashed on a scheduled domestic flight in DhakaEast Pakistan.
On 25 October 1973, a Greenlandair S-61N, OY-HAI "Akigssek" ("Grouse") crashed about 40 km south of Nuuk, resulting in the loss of 15 lives. It was en route to Paamiut from Nuuk. The same aircraft had an emergency landing on the Kangerlussuaq fjord two years earlier, due to flameout on both engines because of ice in the intake.
On 10 May 1974 KLM Helikopters S-61N PH-NZC crashed en route to an oil rig in the North Sea. None of the two crew and four passengers survived. The probable cause was a failure in one of five rotor blades due to metal fatigue. The resulting imbalance caused the motor mounts to fail and caused a fire. The uncontrollable aircraft landed hard in the water, capsized and sank. Investigation indicated that the metal fatigue crack must have spread rapidly in less than four hours. The rotor blades are pressurized with nitrogen gas at 10 psi to indicate the onset of a metal fatigue failure, yet no pressure loss was indicated during the preflight inspection. As a result of the accident it was recommended to shorten inspection intervals The aircraft was recovered from the North Sea floor. It was rebuilt and currently flies as registration N87580 in the USA.
On 16 May 1977, New York Airways' commercial S-61-L, N619PA, suffered a static rollover onto its starboard side at the heliport on top of the Pan Am Building while boarding passengers. The accident killed four boarding passengers and one woman on the street. 17 additional passengers and the three flight crew members were uninjured. The landing gear collapse was a result of metal fatigue in the helicopter's main landing gear shock-absorbing strut assembly, which caused the helicopter to tip over without warning. The accident resulted in the permanent closure of the Pan Am Building heliport. As the heliport was closed, the wreckage was removed by disassembling it and taking the assemblies down to street level using the building's freight elevators. The airframe was taken to Cape Town, South Africa, where it was rebuilt, certified and returned to service as the first S61 used in the Ship-Service Role off the shores of the Western Cape by the company "Court Helicopter" which was later amalgamated with CHC.
On March 20, 1985, an Okanagan Helicopters S-61N (C-GOKZ) ditched in the Atlantic Ocean off of Owl's Head, Nova Scotia. The aircraft was en route from the MODU Sedco 709 offshore Nova Scotia to the Halifax International Airport(YHZ)when the main gearbox suffered a total loss of transmission fluid. There were 15 passengers and two crew on board. There were no injuries during the ditching, however several passengers suffered varying degrees of hypothermia. As a result of this incident, improved thermal protection and other advancements in helicopter transportation suits were instituted for offshore workers on Canada's east coast.
On 5 August 2008, two pilots and seven firefighters assigned to the Iron Complex fire in California's Shasta-Trinity National Forest, were killed when Carson Helicopters S-61N N612AZ crashed on takeoff. Of the 13 people reportedly on board, one other pilot and three firefighters survived the crash with serious or critical injuries. The NTSB determined that the probable causes were the following actions by Carson Helicopters: 1) the intentional understatement of the helicopter's empty weight, 2) the alteration of the power available chart to exaggerate lift capability, and 3) the use of unapproved above-minimum specification torque in performance calculations that, collectively, resulted in the pilots' relying on performance calculations that significantly overestimated load-carrying capacity and without an adequate performance margin for a successful takeoff; and insufficient oversight by the U.S. Forest Service and the Federal Aviation Administration. Contributing factors were the flight crew's failure to address the fact that the helicopter had approached its maximum performance capability on two prior departures from the accident site as they were accustomed to operating at its performance limit. Contributing to the fatalities were the immediate, intense fire due to a fuel spillage upon impact from the fuel tanks that were not crash-resistant, the separation from the floor of the cabin seats that were not crash-resistant, and the use of an inappropriate release mechanism on the seat restraints.
Specifications (S-61N Mk II)
Data from International Directiory of Civil Aircraft
^UPI. Helicopter Crash Kills Five. Beaver County (Pa.) Times: Tuesday, 17 May 1977, A-13.
^Schneider, Daniel B. "F.Y.I.", July 25, 1999. Accessed September 30, 2007. "Q. Back in the 1960s and 70s, helicopters bound for Kennedy International Airport used to take off from a deck atop the old Pan Am Building. Why was the service halted? A. As many as 360 helicopter flights a day were planned by New York Airways after the 59-story Pan Am building was completed in 1963, but a bitter public outcry delayed the first few flights until December 21, 1965 ... The operation proved unprofitable, however, since the helicopters carried an average of only eight passengers, and the heliport, which had cost $1 million to build, closed in 1968 ... After another round of hearings - and renewed protests - flights resumed in February 1977. Three months later, the landing gear on one of the Sikorsky S-61 helicopters collapsed while passengers were boarding, flipping it on its side and sending a 20-foot rotor blade skidding across the roof and over the west parapet wall ... Within hours, the heliport was closed indefinitely."
^"FAA/NTSB Investigations". Los Angeles Injury Law Firm (See post #4 titled "Nine Firefighters Believed Dead After Helicopter Crash in California"). 2008-08-06. Archived from the original on 2007-06-24. Retrieved .