IN FOCUS: The TriStar heritage 40 years on

Forty years ago, in April 1972, Lockheed saw its last civil airliner design - the L-1011 TriStar - enter service with launch customer Eastern Airlines.

The TriStar was one of several newly designed airliners, produced in a period of unprecedented innovation, that still influence commercial aviation. The 1960s had seen jet and turboprop propulsion technology mature, which marginalised the remaining big piston-engined airliners and created the potential for much larger aircraft with shorter sector times and lower seat-mile costs.

By 1983, Lockheed had halted production of the type. Today, of the 249 TriStars that rolled off Lockheed's purpose-built production line in Palmdale, California, about 11 remain in service, according to Flightglobal's Ascend database. Seven of those are with the UK Royal Air Force.

In 1970, the year the first TriStar was rolled out, Boeing had seen its massive 747 - providing more than twice the passenger capacity of existing jets such as the 707 - go into operation with Pan American World Airways. At service entry, the 747 was actually too big for its time, but the aircraft had nevertheless been successfully launched into the civil market on the back of Boeing's bid for a US military heavy-lift freighter contract that the 747 lost to Lockheed's C5A Galaxy.

In 1965 and 1966 respectively, McDonnell Douglas (MDC) and Lockheed began researching potential demand for second-generation jets to serve the huge US domestic airline commercial passenger market. Exploratory talks with the carriers led the two manufacturers to pitch for similar capacities and performance in this sector, which was a phenomenally healthy and fast-growing marketplace at the time.

Across the Atlantic, a new multinational manufacturing venture called Airbus Industrie was planning its entry into the same market sector with a short-/medium-haul widebody twinjet, the A300. At the same site in Toulouse, France, as Airbus, co-operating in another multinational civil airliner project, Aerospatiale was working with the British Aircraft Corporation to prepare the supersonic Concorde for flight.

At that time, the US market's need for short-haul narrowbody aircraft was already well served by the new Boeing 737 (in service 1968) and the better-established MDC DC-9 series, so both Lockheed and MDC found themselves addressing the medium-haul marketplace and looking to take advantage of new, more powerful high-bypass jet engines to provide greater passenger capacity.

Lockheed's first reaction was to pitch for a big twin, because American Airlines, with which both Lockheed and MDC were talking, wanted a high-capacity, low-cost type. But when the manufacturer began to dig deeper into the airline requirements, it became clear that with demand for twin-aisle capacity, US transcontinental range and the ability to clear the Rocky Mountains after take-off from the US West Coast eastward, the engines of the day were not going to fulfil the wish list with any fewer than three power units on an aircraft of the capacity required. The other incidental advantage of a third engine was compliance with the extended range over water performance requirements of the time, which was very limiting for twins.

When American Airlines chose the DC-10, because its initial version suited its commercially critical New York LaGuardia-Chicago overland route, Lockheed began to diverge towards the longer-range specifications of carriers such as Eastern Airlines, whose defining routes were transcontinental and over water. With these two close US competitors in the field, as wekk as Boeing's 747 and the Airbus A300 beginning to take shape as a commercial reality, the marketplace was skewed heavily in the buyers' favour, putting massive pressure on price pitching.

Eastern eventually became the TriStar's launch customer, signing a letter of intent in New York on 29 March 1968 along with Trans World Airlines. When the programme was launched two days later, the decision was taken on the back of commitments to 144 aircraft: 50 for Eastern, 44 for TWA and 50 for Air Holdings, a financial vehicle designed to support the sale of export aircraft. Other early customers with substantial orders included Air Canada, Cathay Pacific, Gulf Air, British European Airways, All Nippon Airways and Delta Airlines. Later came Saudia, British Airways and United Airlines, while many other carriers placed smaller orders.

The launch version of the TriStar, the L1011-1, could accommodate 227 passengers in mixed class or 300 in economy and carry them from coast to coast, but the machine had been designed from the beginning for expansion in both performance and size. Its range with a full passenger payload was about 2,700nm (5,000km), whereas later variants would extend this to 5,000nm.

On the same day as Eastern and TWA announced their commitment, Rolls-Royce was named as the sole engine supplier for the TriStar, with its promising and revolutionary but relatively untried - three-spool RB211 high-bypass turbine engine, sporting a composite material fan. All R-R's competitors in this market sector fielded twin-spool engines - and still do. Although R-R had been dallying with the three-spool idea for some years, the RB211 was only launched as a definite project in 1967. Lockheed was to begin assembly of its first L1011-1 in March 1969, but the RB211 only demonstrated its target power of 40,600lb thrust for the first time by the end of that year.

The RB211's technical promise was undoubtedly an attraction for Lockheed, but Pratt & Whitney or General Electric could have supplied engines for the TriStar. Indeed, GE's new CF6 series engine - derived from its TF39 turbofan, which had powered the C5A - was chosen for the first DC-10s off the MDC production line. GE offered the CF6 series engine to Lockheed, too, whereas P&W was occupied with supplying its JT9 series engines for the 747 series, and a version of the powerplant for the TriStar would have needed downrated thrust and a fan diameter change.

This deal between Lockheed and R-R was momentous, for R-R in particular and British industry in general, but was to be the cause of much heartache in political, business and engineering terms on both sides of the Atlantic for the next four years. The successes of a new engine and new airframe were never more completely interdependent than the RB211 and the L1011 TriStar.

During that period R-R lurched into receivership, before being bailed out by a Conservative government that had sworn it would do no such thing, and consequent delays to the TriStar project meant it almost had to be cancelled. Lockheed itself was struggling with cost overruns on the C5A military project, and in 1970 had to ask for advance payments to save the company. Meanwhile the DC-10 project steamed ahead and by the time the TriStar went into service, MDC was ready to launch a long-range version, the -30, that exceeded the TriStar's range performance - until the longer-legged L1011-500 version entered service in 1979.

Despite all this, the TriStar test programme never actually stopped. The aircraft had been rolled out at Palmdale on 1 September 1970, and the maiden flight took place on 16 November, powered by a pre-production set of RB211 engines rated at 40,600lb thrust. The aircraft and engines performed well on the 140min flight.

In fact, Rolls-Royce's bench and flight test programme for the engine had gone remarkably well for a design embodying so many changes from the engineering conventions of the time. The engine's early flights were made on a BAC (Vickers) VC-10 loaned by the RAF, with the test RB211 replacing the left pair of rear-mounted R-R Conway turbojets.

The RB211 programme's agonies were almost entirely centred around the Hyfil composite fan blades, which were performing well under normal circumstances throughout the flight regime, but proved vulnerable to grit erosion, which allowed water to penetrate, causing delamination. Also unacceptable was the fact that the Hyfil blades did not perform adequately in bird impact tests.

Rolls-Royce developed a series of expensive and time-consuming fixes for these problems, with varying degrees of success, but in the end was forced to adopt the plan B that it had always kept in reserve: fitting a titanium fan. Unfortunately, this added 300lb to the engine's weight and reduced its performance and fuel efficiency. The Hyfil fans never went into commercial service in the TriStar.

In February 1971, Rolls-Royce was declared insolvent. The TriStar test programme at Palmdale had been running well, but fears about engine supplies slowed development to a crawl. Meanwhile Lockheed had negotiated its own financial support to keep the programme going, and quite quickly the UK government moved to nationalise R-R, which saved the RB211 programme. R-R then renegotiated its engine contract with Lockheed, so the TriStar project was back on the rails.

All stages of the TriStar's airborne test programme went smoothly, with only minor snags to sort out, proving the basic soundness of the airframe and engine manufacturers' work. Certification for the production engine - the RB211-22C rated at 42,000lb thrust - came from the UK Air Registration Board and the US Federal Aviation Administration on 22 March 1972, and from the FAA for the airframe/engine combination less than a month later on 15 April. This was five months later than planned, which seems a minor delay compared with programmes this century such as the A380 and the 787, and the fact that the world's first oil crisis (in 1971) had depressed the economy at the time meant the airlines were not champing at the bit for on-time delivery.

Although the RB211 in the TriStar did not achieve its highly optimistic fuel efficiency target, fuel consumption was nevertheless a considerable improvement on previous performance, which was welcome as the world woke up to the fact that oil-based fuels were a finite resource. It also made the TriStar the quietest jet then flying, allowing Lockheed to dub it the Whisperjet. And the TriStar, uniquely at the time, was certificated from service entry for Cat 3a autoland, giving it a considerable bad-weather advantage over the DC-10 and 747.

During its service life the TriStar rapidly advanced through several variants as the engines developed and airframe improvements became available. Several variants - the -50, 150 and 250 - were upgrades to the original L1011-1s. The -100 and -200 came off the production line with more powerful engines cleared for higher gross weight operation. The biggest leap came with the introduction of the -500, launched in 1976, which took the Tristar into a new market sector by improving its range considerably. This led to it competing directly - for the first time - with the DC-10-30 and 747. It had a slightly shortened fuselage, longer wingspan with active ailerons for gust alleviation, and improved aerodynamics, and was fitted with RB211-524 engines delivering 50,000lb thrust. In British Airways' hands, the TriStar 500 achieved full Cat IIIb zero-decision-height autoland capability.

The BA TriStar 500s were also fitted with a flight management system (FMS) that worked in the vertical as well as the horizontal sense, allowing accurate area navigation and reduced fuel consumption. The FMS navigation input was from a triplex inertial navigation system updated by inputs from ground-based beacons such as VOR/DME.

The TriStar was, in many respects, more technically advanced than its US competitors, the 747 and DC-10, but its limited commercial success in a crowded marketplace caused Lockheed to abandon the civil marketplace after stopping L1011 production in 1983. That Lockheed project, however, was the sole basis for the successful development of the Rolls-Royce RB211 series of engines and the continued existence of R-R aero engines. The successor to the RB211 series - the Trent series - is one of the most successful big fan families in the world today.

SAFETY IN OPERATION

The global TriStar fleet has suffered three fatal hull-loss accidents during flight operations, but none of them was judged to be the result of faulty design in the airframe or engine, nor of a technical failure.

The first, in December 1972, involved an Eastern Airlines L1011-1 on a night approach to Miami. There was an indication that the nose-gear had failed to lock down and the crew elected to go around, climb to 2,000ft and investigate the warning. While they were carrying out the checks, one of the pilots knocked the control yoke, disengaging the autopilot, but no-one noticed it had disengaged. So fixated were the crew on attempting to fix the nosewheel-down indicator light that they failed to monitor the aircraft's performance and it slowly descended to crash in the Everglades swamps, killing 99 of the 176 people on board.

Saudi Arabian Airlines suffered an L1011-200 accident in August 1980. It was a horrifying event which, to this day, leaves questions unanswered, but most of these concern the actions and decisions of the captain. There was a fire alert from the rear cargo as the aircraft was climbing out of Riyadh for Jeddah on a Hajj flight with 301 people on board. Soon afterwards smoke was reported in the cabin. No emergency was declared and it took the captain five minutes to make the decision to return to Riyadh to land. The fire entered the cabin and melted the control connections to the tail engine, which the captain shut down. But upon landing the captain did not order immediate evacuation, and when the fire crews opened the doors, the cabin had already been consumed by fire and everybody was dead.

In August 1985, a Delta Airlines L1011-1 was caught in a severe downburst associated with thunderstorm activity on short final approach to Dallas/Ft Worth. The crew attempted to go around, but the aircraft was driven into the ground, killing 134 of the 163 people on board. This accident did more than any other to accelerate research into the physics of storm-related windshear, and to spur the development of windshear-warning equipment.

RAF TRISTARS RACK UP PHENOMENAL MISSION SUCCESS RATE

In the early 1980s, the RAF's fleet of Victor tankers was nearing the end of its life, and the decision was taken to augment and then replace them with converted airliners. Nine VC10s were acquired from Gulf Air and BAE (ex East African Airlines aircraft) and converted to three-point tanker configuration from 1982. It was planned that further VC10s would be converted to tanker configuration later, when the Victors were retired.

But the Falklands War and the subsequent "air bridge" used up Victor fatigue life more quickly than planned, and in December 1982, six ex-British Airways Lockheed L-1011-500 TriStars were purchased. These initially operated in the strategic transport role as TriStar C.Mk 1 passenger aircraft.

© Sunshine Band/AirSpace The RAF purchased six ex-British Airways TriStars in 1982

The first RAF aircrew began training at RAF Brize Norton in August 1983, and were fully qualified by February 1984. 216 Squadron was officially reformed in November 1984, and the squadron began flying a thrice-weekly schedule to the Falkland Islands in December 1985.

Three ex-Pan Am L-1011-500 TriStar aircraft were purchased in 1984. Two entered service as TriStar C.Mk 2 passenger aircraft, carrying 260 passengers and up to 16 tonnes of freight. One of the ex-Pan Am aircraft was stored before being upgraded with military radios and avionics, becoming the sole C.Mk 2A.

The ex-British Airways TriStars were subsequently converted to tanker configuration by Marshal of Cambridge, although the TriStar's unusually flexible outer wing and active ailerons mitigated against the fitting of underwing hose drum unit (HDU) pods, limiting the aircraft to a "single point" configuration, albeit with two centreline HDUs to provide a degree of redundancy. A CCTV system was installed under the rear fuselage to monitor refuelling, and underfloor fuel tanks were added, increasing available fuel by 43,900kg (96,600lb) bringing the total to 139,700kg.

Two were converted as K.Mk 1 tanker/transports, with 187 seats in the rear cabin, and baggage forward. The remaining four were brought to KC.Mk 1 standards, with a large, fuselage freight-door, a reinforced floor and a roller-conveyor system fitted to allow the carriage of up to 31 tonnes of palletised cargo and/or up to 160 passengers.

The first TriStar tanker entered service with the squadron in 1986 and has played its part in the RAF's post Cold War conflicts. For operation Granby (the 1991 Gulf War) the two K.Mk 1s were hastily painted in desert pink camouflage and deployed to King Khalid International Airport, near Riyadh. Named "Pinky" and "Perky", they flew more than 90 AAR missions, accumulating more than 430 flying hours and transferring 3,100,00kg of fuel.

AAR SUPPORT

Subsequently, the 216 Sqn TriStars deployed to Ancona, Italy to provide AAR support for NATO fighters enforcing the no-fly zone over Bosnia-Herzegovina. Then during Operation Allied Force (the 1999 Kosovo war) the TriStars were again involved. Five tankers flew 230 missions with a 100% success rate; transferring 13.5 million lb of fuel to 1,580 aircraft from seven countries.

216 Sqn supported Operation Resinate South (the southern Iraqi no-fly zone operation) between August 2001 and March 2003, operating from Bahrain, and then participated in Operation Veritas (Afghanistan) in 2003, providing AAR support for US Navy fast jets. A 216 Sqn TriStar was the first Allied tanker to enter Afghan airspace.

© RAF TriStar RAF TriStars will be replaced in 2014

The TriStars flew about 300 AAR missions during Operation Telic in 2003 (Iraq), and extensive "air bridge" missions to Iraq and Afghanistan. Most recently, TriStar tankers supported Operation Ellamy (the British part of coalition operations in Libya to enforce UN Resolution 1973).

The TriStars have been progressively updated and have received joint tactical information distribution system datalink terminals, flightdeck armour and enhanced defensive aids, including directional infrared counter measures systems. The aircraft are also being fitted with an updated glass cockpit.

As an alternative to the £13 billion ($21 billion) Future Strategic Tanker Aircraft (FSTA) programme, Marshall Aerospace made a proposal to adapt second-hand ex-airline TriStars to tanker configuration to provide a much-needed increase in refuelling capacity at a low cost.

The RAF TriStars are due to be replaced by Airbus A330 MRTT Voyagers being delivered under the FSTA PFI programme. The TriStar's out-of-service date was brought forward to 2014.

Source: Flight International