Sikorsky S-61

The Sikorsky S-61L and S-61N are civil variants of the successful Sikorsky SH-3 Sea King helicopter. They are two of the most widely used airliner and oil rig support helicopters built.[1]

This article is about the civil versions of the Sikorsky S-61 models. For the military versions, see Sikorsky SH-3 Sea King.
S-61L/S-61N
A S-61N Mk.II operating for Sociedad de Salvamento y Seguridad Marítima in Spain
Role Medium-lift transport / airliner helicopter
Manufacturer Sikorsky Aircraft
First flight March 11, 1959
Introduction September 1961
Status Active service
Primary users CHC Helicopter
Bristow Helicopters
AAR Airlift
Number built 119[1]
Developed from Sikorsky SH-3 Sea King

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.[1] 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.[1] The S-61L first flew on 2 November 1961, and was 4 ft 3 in (1.30 m) longer than the HSS-2 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,[2] introducing them on 11 March 1962, for a purchased price of $650,000 each.[3]

From 1962 to 1966, PIA operated its Sikorsky S-61 helicopters for services within East Pakistan Helicopter Service (present day Bangladesh) used Four S-61s. The helicopter route to Khulna reduced the 21-hour journey overland to 37 minutes by air. 20 towns and cities covered by the network, including Bogra, Sirajganj, Chittagong, Mongla, Kushtia, Barisal, Chandpur, Sandwip and Hatiya Upazila. The average price of a ticket was 25 rupees. It was the world's largest commercial helicopter network at the time.[4]

On 7 August 1962, the S-61N made its first flight.[1] 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 refinements.

The Payloader, a stripped-down version optimized for aerial crane work, was the third civil model of the S-61.[1] 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.[5]

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.[1] 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).[5]

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 US Embassy in Afghanistan.[6]

Variants
S-61L
Non-amphibious civil transport version. It can seat up to 30 passengers[7]
S-61L Mk II
Improved version of the S-61L helicopter, equipped with cargo bins.[8]
S-61N
Amphibious civil transport version.[7]
S-61N Mk II
Improved version of the S-61N helicopter.[8]
S-61NM
An L model in an N configuration.[9]
S-61T Triton
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[10]

Operators
A Netherlands Coastguard S-61L operated by Bristow Helicopters
 Canada
 Greenland
 Lebanon
 United Kingdom
 Spain

 United States

A British International Helicopter S-61N lands aboard the USS Vicksburg

Former operators
 Canada
 Ireland
 Netherlands
A Carson Helicopters Sikorsky S-61N
 Norway
 Pakistan (1962 to 1966)
 United Kingdom
 United States

Notable accidents
N300Y, the Los Angeles Airways prototype of the Sikorsky S-61L Helicopter, lifting off from the Disneyland Heliport

1960s

1970s

  • 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.[42]
  • 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[43] The aircraft was recovered from the North Sea floor. It was rebuilt and currently flies as registration N87580 in the USA.[44]
  • 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.[45] 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.[46] 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.[47]

1980s

  • On 16 July 1983, British Airways Helicopters' commercial S-61 G-BEON crashed in the southern Celtic Sea, in the Atlantic Ocean, while en route from Penzance to St Mary's, Isles of Scilly in thick fog. Only six of the 26 on board survived. It sparked a review of helicopter safety and was the worst civilian helicopter disaster in the UK until 1986.
  • 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.
  • 12 July 1988 a British International Helicopters S-61N ditched into the North Sea, no injuries.

1990s

2000s

  • On 8 July 2006, a Sociedad de Salvamento y Seguridad Marítima S-61N Mk.II search and rescue helicopter, crashed into the Atlantic Ocean while it was flying from Tenerife to La Palma. There were no survivors among the six people on board.
  • 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.[49][50][51]

Specifications (S-61N Mk II)
Orthographically projected diagram

Data from International Directiory of Civil Aircraft[1]

General characteristics

  • Crew: 2
  • Capacity: up to 30 passengers
  • Length: 58 ft 11 in (17.96 m)
  • Height: 17 ft 6 in (5.33 m)
  • Empty weight: 12,336 lb (5,596 kg)
  • Gross weight: 16,164 lb (7,332 kg)
  • Max takeoff weight: 19,000 lb (8,618 kg)
  • Powerplant: 1 × General Electric CT58-140 turboshaft engines, 1,500 shp (1,100 kW)
  • Main rotor diameter: 62 ft (19 m)
  • Main rotor area: 3,019 sq ft (280.5 m2)
  • Blade section: - NACA 0012[52]

Performance

  • Maximum speed: 144 kn (166 mph, 267 km/h)
  • Cruise speed: 120 kn (140 mph, 220 km/h)
  • Range: 450 nmi (520 mi, 830 km)
  • Service ceiling: 12,500 ft (3,800 m)
  • Rate of climb: 1,310–2,220 ft/min (6.7–11.3 m/s)
gollark: There are mods for it. I don't know if you can do it on 1.14.4 with the mess going on with that.
gollark: The Minecraft one.
gollark: It would be cool if the server had some mod or other to bridge its chat to a Discord channel here.
gollark: It should work if you don't go around building loads of stuff.
gollark: Though your CPU is worse than that, I guess.

See also

Related development

References
  1. Frawley, Gerard: The International Directory of Civil Aircraft, 2003–2004, p. 194. Aerospace Publications Pty Ltd, 2003. ISBN 1-875671-58-7.
  2. Apostolo, G. "Sikorsky S-61".The Illustrated Encyclopedia of Helicopters. Bonanza Books, 1984. ISBN 0-517-43935-2.
  3. "The Self-Supporting Helicopter" Time Magazine December 26, 1960
  4. "Asia: Choppers over Pakistan". 13 December 1963. Retrieved 14 September 2017 – via content.time.com.
  5. Carson Helicopters (2009). "About Carson Helicopters". Retrieved 2009-01-12.
  6. Press Releases: U.S. State Department Accepts Modernized S-61TM Helicopters for Use in Afghanistan
  7. "VTOL AIRCRAFT 1967 pg. 712". Flightglobal Insight. 2015. Retrieved 4 January 2015.
  8. "CIVIL V/STOL 1971 pg. 162". Flightglobal Insight. 2015. Retrieved 4 January 2015.
  9. "Airworthiness Directives Sikorsky Models S-61L, S-61N, and S-61NM". faa.gov. Retrieved 12 January 2015.
  10. Reed Business Information Limited. "HELI-EXPO: Sikorsky S-61T gains new life in State Department program". Flight Global. Retrieved 4 January 2015.
  11. "CHC Helicopter fleet". chc.ca. Archived from the original on 13 February 2013. Retrieved 17 March 2013.
  12. "Cougar Helicopters". cougar.ca. Archived from the original on 24 August 2013. Retrieved 17 March 2013.
  13. "Air Greenland fleet". airgreenland.com. Retrieved 17 March 2013.
  14. "World Air Forces 2013" (PDF). Flightglobal Insight. 2013. Retrieved 17 March 2013.
  15. "Bristow Helicopters fleet". bristowgroup.com. Retrieved 17 March 2013.
  16. http://www.salvamentomaritimo.es/sm/flota-y-medios/medios-aereos/helicopteros-de-salvamento-maritmo/?ids=358
  17. "DOD Contracts Keep U.S. Helicopter Operators Busy in Afghanistan". ainonline.com. Retrieved 4 June 2013.
  18. "Carson Helicopters Home page". carsonhelicopters.com. Retrieved 17 March 2013.
  19. "Former employees of Carson Helicopters indicted over fatal Iron 44 Fire crash". wildfiretoday.com. Retrieved 17 March 2013.
  20. CHI Aviation. "Fleet". Retrieved 20 May 2019.
  21. Helimax Aviation. "Fleet". Retrieved 20 May 2019.
  22. "Croman Corporation Heavy Lift Svc". croman.net. Archived from the original on 4 March 2013. Retrieved 17 March 2013.
  23. "Helicopter Transport Services Aircraft". htshelicopters.com. Retrieved 17 March 2013.
  24. "Sikorsky". www.sikorsky.com. Retrieved 14 September 2017.
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  27. "End Of An Era As Irish Coast Guard's Last S61 Retires". afloat.ie. Retrieved 12 December 2013.
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  31. "Helicopter Service". Retrieved 26 June 2019.
  32. "World Helicopter Market 1967 pg. 63". flightglobal.com. Retrieved 4 February 2016.
  33. "British Airways Helicopters". Retrieved 17 March 2013.
  34. "British Caledonian Helicopters". Retrieved 26 June 2019.
  35. "British International Helicopters S-61". Retrieved 17 March 2013.
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  37. "Flight Int'l 1969 Pg. 581". flightglobal.com. Retrieved 17 March 2013.
  38. "New York Airways". flightglobal.com. Retrieved 17 March 2013.
  39. "World Helicopter Market 1968 pg. 57". flightglobal.com. Retrieved 5 February 2016.
  40. "PIA helicopter service". Retrieved 2019-02-14.
  41. Aircraft Accident Report. Los Angeles Airways, Inc. S-61L Helicopter, N300Y, Compton, California Archived 2008-06-25 at the Wayback Machine, Adopted: August 27, 1969
  42. "Arktisk dokumentarkiv". arktiskleksikon.dk. Archived from the original on 14 December 2014. Retrieved 4 January 2015.
  43. "1974". hdekker.info. Retrieved 4 January 2015.
  44. Harro Ranter. "ASN Aircraft accident 10-MAY-1974 Sikorsky S-61N PH-NZC". aviation-safety.net. Retrieved 4 January 2015.
  45. UPI. Helicopter Crash Kills Five. Beaver County (Pa.) Times: Tuesday, 17 May 1977, A-13.
  46. 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."
  47. Epstein, Curt. HAI Convention News "An S-61 With a Past" October 26, 2010. Retrieved: June 13, 2011.
  48. UK Air Accidents Investigation Branch, Department of Transport, Report on the Accident to Sikorsky S-61N G-BEWL at Brent Spar, East Shetland Basin on 25 July 1990, retrieved 4 January 2014
  49. "Aircraft Accident Report Crash During Takeoff of Carson Helicopters, Inc., Firefighting Helicopter Under Contract to the U.S. Forest Service, Sikorsky S-61N, N612AZ Near Weaverville, California August 5, 2008 NTSB/AAR-10/06". ntsb.gov. Retrieved 14 September 2017.
  50. "USFA Fatality Notice". United States Fire Administration. 2008-08-06. Archived from the original on 2008-09-17. Retrieved 2008-08-11.
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  52. Lednicer, David. "The Incomplete Guide to Airfoil Usage". m-selig.ae.illinois.edu. Retrieved 16 April 2019.
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