The Pratt & Whitney JT8D is a low-bypass (0.96 to 1) turbofan engine introduced by Pratt & Whitney in February 1963 with the inaugural flight of the Boeing 727. It was a modification of the Pratt & Whitney J52turbojet engine which powered the US NavyA-6 Intruder and A-4 Skyhawkattack aircraft. Eight models comprise the JT8D standard engine family, covering the thrust range from 12,250 to 17,400 pounds-force (54 to 77 kN), and power the 727, 737-100/200, and DC-9. The updated JT8D-200 family, covering the 18,900 to 21,000 pounds-force (84 to 93 kN), powers the MD-80 and re-engined Super 27 aircraft. The JT8D was built under license in Sweden as the Volvo RM8, a redesigned afterburning derivative for the Saab 37 Viggen fighter.[2] Pratt & Whitney also sells static versions for powerplant and ship propulsion as the FT8.
Design
Cutaway showing the configuration: twin fan, axial compressor stages, cannular combustors and 4-stage turbine
The JT8D is an axial-flow front turbofan engine incorporating a two-spool design. There are two coaxially-mounted independent rotating assemblies: one rotating assembly for the low pressure compressor (LPC) which consists of the first six stages (i.e. six pairs of rotating and stator blades, including the first two stages which are for the bypass turbofan), driven by the second (downstream) turbine (which consists of three stages); and a second rotating assembly for the high-pressure compressor (HPC) section, which has seven stages. The high-pressure compressor is driven by the first (upstream) turbine, which has a single stage.
The front-mounted bypass fan has two stages. The annular discharge duct for the bypass fan runs along the full length of the engine, so that both the fan air and exhaust gases can exit through the same nozzle. This arrangement allows some noise attenuation, in that the still-hot fast-moving turbine exhaust is shrouded in much-cooler and slower-moving air (from the bypass fan) before interacting with ambient air. Thus, the JT8D noise levels were significantly reduced from previous non-turbofan engines, although the low bypass ratio meant that, compared to subsequently developed turbofans, high noise levels were still produced.
Within the fan inlet case, there are anti-icing air bosses and probes to sense the inlet pressure and temperature. Similar units exist throughout the engine to check temperatures and pressures.
At the 13th (i.e. the final) compressor stage, air is bled out and used for anti-icing. The amount is controlled by the Pressure Ratio Bleed Control sense signal (PRBC). The diffuser case at the aft end of the compressor houses the 13th stage. Its increasing cross-sectional area allows the compressed air to slow down before entering one of the engine's nine burner cans. Again, there are two bosses to extract 13th stage air for anti-icing, de-icing of fuel, and airframe (cabin pressurization) use. Not all the compressed air enters the burner cans at the fuel-ignition point; some bypasses the can completely and cools the first turbine stage, and some is gradually introduced into the burner can's perimeter in such a way that the burning fuel is held near the can's centerline.
There are nine combustion chambers positioned in a can-annular arrangement. Each chamber has three air inlet hole sizes: the smallest is for cooling, the medium is for burning and the largest for forming an air blanket.
In response to environmental concerns that began in the 1970s, the company began developing a new version of the engine, the JT8D-200 series.[3] Designed to be quieter, cleaner, more efficient, yet more powerful than earlier models, the -200 Series power-plant was re-engineered with a significantly higher bypass ratio (1.74 to 1) covering the 18,500 to 21,700 pound-force (82 to 97 kN) thrust range and powering the McDonnell Douglas MD-80 series. This increase was achieved by increasing bypass fan diameter from 39.9 inches (101 cm) to 49.2 inches (125 cm) and reducing fan pressure ratio (from 2.21 to 1.92).[citation needed] Overall engine pressure ratio was also increased from 15.4 to 21.0.[4] Since entering service in 1980, more than 2,900 of the -200 series engines have been produced.
The JT8D-217 and -219 engine(s) were tested in 2001 and were deemed suitable replacements for the old TF33 engines on military and commercial aircraft as part of the Super 27 re-engining program. The updated engines offer reduced (Stage-3) noise compliance standards without the need for hush kits, enhanced short field performance, and steeper and faster climb rates with roughly a 10% reduction in fuel burn for extended range.
Pratt & Whitney, in a joint venture with Seven Q Seven (SQS) and Omega Air, developed the JT8D-219 as a re-engine powerplant for Boeing 707-based aircraft.[5] Northrop Grumman used the -219 to re-engine one of the United States Air Force's fleet of 19 Joint Surveillance Target Attack Radar System (E-8 Joint STARS) aircraft, which would allow the JSTARS more time on station due to the engine's 17% [6] greater fuel efficiency. However these plans were cancelled after the single conversion when the decision was taken to retire the platform. NATO originally planned to re-engine their fleet of E-3 Sentry AWACS aircraft, however again this was cancelled after the decision was taken to retire the E-3 platform in preference for the E-7 Wedgetail. The -219 is publicized as being half the cost of the competing 707 re-engine powerplant, the CFM International CFM56, for reasons of geometrical and balance similarity to the engine it is replacing and the associated relative up-front wing modification costs of the two choices.[5][6]
More than 14,000 JT8D engines have been produced, totaling more than one-half billion hours of service, with more than 350 operators, making it the most popular of all low-bypass turbofan engines ever produced.[9][1] Regular production ended in 1985, but some replacement engines were produced for military aircraft in 2011.[10]Mainline airline use of the JT8D continued until 2020 when Delta Air Lines retired their MD-88 fleet early due to the COVID-19 pandemic.[11]
United Airlines Flight 266 – ten minutes after takeoff, the cockpit received a warning from Engine 1 of an engine fire and cut off power to that engine. A minute later, Flight UA266 suffered a total loss of electrical power, which disabled the aircraft's flight instruments. At 13 minutes after take-off, the plane crashed into the Pacific Ocean, just 12 miles off the coast, killing all 38 people aboard the aircraft, which consisted of 32 passengers and 6 crew members.
4 April 1977
Southern Airways Flight 242 – both engines on the DC-9 failed when the pilots flew into a severe thunderstorm after misreading their onboard radar. The flight encountered severe rain and hail. The NTSB concluded that the "loss of thrust was caused by the ingestion of massive amounts of water and hail which in combination with thrust lever movement induced severe stalling in and major damage to the engine compressors". Some 63 people on board and nine on the ground died as a result of the accident.
Midwest Express Flight 105 – the NTSB concluded that an unconfined failure of the 9th - 10th stage compressor spacer occurred immediately after takeoff from Milwaukee Mitchell International Airport (then called Billy Mitchell Field). The plane was observed to have slowed significantly as a result of the engine loss and experienced an accelerated stall condition. The plane rolled to the right 90 degrees and crashed just south of the runway, resulting in 31 fatalities (all passengers and crew) aboard the McDonnell-Douglas DC-9 aircraft.[13]
3 May 1991
Ryan Airlines – unconfined failure of 9th stage compressor disc penetrated fuel lines and fuselage on the tarmac at Bradley International Airport causing fire and complete loss of aircraft. No fatalities reported.[14]
27 December 1991
Scandinavian Airlines Flight 751 – the engines on an MD-81 ingested wing ice during takeoff causing engine damage that led to a total loss of thrust on both engines. The aircraft crashed in a forest clearing with no fatalities.
A 737-200 operated by Air Algériecrashed due to sudden loss of thrust as a result of the left engine's fan blades fracturing and the captain taking controls off of the first officer without assessing or mentally preparing for the situation. All six crew and 96 of the 97 passengers were killed.
A privately owned MD-87 was recorded on its takeoff roll just after throttling up a "puff of smoke" was observed from the left engine nacelle. Subsequently the aircraft rolled off the end of the runway into a grass field and caught fire. The MD-87 was almost completely destroyed by the resulting fire.[17] The privately owned jet, N987AK McDonnell Douglas MD-87, owned by J. Alan Kent Development LLC,[18] was operating a charter flight carrying sports fans to Boston for the ALCS Championship Baseball Games. Only 1 minor injury and no fatalities occurred in this incident.[19] It is still under active investigation.
^ ab"JT8D". Pratt and Whitney. Archived from the original on 2022-01-25. Retrieved 2021-07-07. The JT8D engine has proven itself to be a highly durable and reliable engine, having completed more than 673 million dependable flying hours since entering service. Once deemed the workhorse of the industry, more than 14,750 JT8D engines have flown. Today, there are 2,400 engines still in use.
^Gunston, Bill (1999). The Development of Piston Aero Engines, 2nd Edition. Sparkford, Somerset, England, UK: Patrick Stephens, Haynes Publishing. p. 169. ISBN0-7509-4478-1.
^"Type Certificate E2EA data sheet"(PDF). Federal Aviation Administration. August 28, 2007. Archived(PDF) from the original on December 28, 2016. Retrieved December 23, 2020.
^"Type Certificate E9NE data sheet"(PDF). Federal Aviation Administration. December 13, 2010. Archived(PDF) from the original on April 19, 2021. Retrieved December 23, 2020.
^"Pratt & Whitney's JT8D Engine Turns Half a Century Old". MediaRoom. Pratt and Whitney. Archived from the original on 2021-07-09. Retrieved 2021-07-07. More than 14,750 JT8D engines have been built, accumulating more than half a billion hours of service. At one point, JT8D engine sales and service contributed about half of United Technologies' profits. Today, it continues to generate revenue through overhauls, spare parts sales and kits to make it quieter and cleaner burning.
Gunston, Bill (1999). The Development of Piston Aero Engines, 2nd Edition. Sparkford, Somerset, England, UK: Patrick Stephens, Haynes Publishing. ISBN0-7509-4478-1.
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