Guy Norris/LOS ANGELES Tables complied by Air Transport Intelligence
Auxiliary Power units (APUs) rarely grab the headlines. Until recent times, any mention of APUs has generally been for the wrong reasons - failures, poor reliability and inadequate support. Now it seems the tide has turned in virtually every aspect of the business and APUs are becoming respectable workhorses. What is more, the fierce competitions in the 100/200-seat market and the inexorable move towards the Airbus A3XX and Boeing 747-X developments have made the APU market an interesting one to watch as 1998 comes to an end.
One of the most intriguing APU-related developments of 1998 was Boeing's decision to study a thrusting APU as a way of reaching higher take-off weight capability with its proposed, ultra-long range 777-200X and -300X versions. The APTU (auxiliary power and thrust unit) study was aimed at filling a perceived 7,000-12,000lb-thrust (30-55kN) gap between the current versions of the 777's engines. The study included consideration of General Electric's CF34-8, a de-rated F414 engine, versions of the BMW Rolls-Royce BR700 family and the Rolls-Royce Allison AE3007. AlliedSignal also offered its new AS900, although the longer development timescale of this new centreline engine made it a more unlikely candidate. The plan was to use the engine in the tail to provide boost power for take-off, but to otherwise use it as a normally functioning APU for the remainder of the flight. Like a similar concept tried in the 1960s by Hawker Siddeley with the Trident, this appears to have created more problems than it solved.
The lessons of the Trident 3, which eventually was given a dedicated RB162 boost engine, seem to have been heeded. By November 1998 the studies appeared to favour the retention of the standard APU (an AlliedSignal 331-500(B)) and the addition of a standalone boost engine for take-off alone. AlliedSignal and GE, which provisionally designated its contender the CF34-8B, are believed to have held talks over a possible joint development of a full propulsion and power package. This was thought to be tailored towards the integration of the 331-500 APU with the CF34, rather than attempting to derive auxiliary power from the CF34, though neither company was prepared to comment.
Meanwhile, Boeing has to choose between the APTU option and higher power main engines which GE is offering in the form of a 112,000lb-thrust GE90. R-R and Pratt & Whitney are still considering their moves, having already committed to growth engines of slightly lesser power for the baseline 777-300 as well as -200X. The airlines, concerned over the potential maintenance headaches and higher costs associated with the APTU, or even the booster engine, have been pushing Boeing towards the latter choice, which the US manufacturer is due to make later this month.
With or without the APTU study, the global APU leader AlliedSignal is already busy with a range of new APU developments. Thanks largely to its Garrett heritage, it also continues with an internal improvement effort which dates from the beginning of the decade, when the airlines accused it of complacency. One manufacturer which took advantage was Auxiliary Power International (APIC), now wholly owned by Sundstrand. The resulting competitive battle between the two continues unabated on the Airbus single-aisle family and, to a lesser extent, on the Boeing 737 "Classic" series which is being produced in smaller numbers and is scheduled to be phased out by 2001.
AlliedSignal raised the stakes on the Airbus battle to new heights with the successful development and introduction of the 131-9(A) on the Airbus single aisle family. The first production APUs began arriving in Toulouse and Hamburg in June and any A319, A320 or A321 delivered after September was available with the 131-9.
The 131-9 is AlliedSignal's flagship APU for single-aisle products and, despite the forthcoming closure of the MD-90 line, is expected to be produced at the record rate of around 300 a year from 1999 onwards. This is largely due to the massive demand from the Next Generation 737 market, but will increasingly include units destined for the Airbus lines as the last of the 36-300 Series have been phased out of production.
The 131-9, originally derived from the unit developed for the Northrop Grumman B-2 bomber, is the first APU to incorporate a starter generator. This eliminates the starter motor and, more importantly from a maintenance and cost perspective, the often troublesome clutch and gearbox.
The 131-9(A) was an almost inevitable development after some major Airbus customers voted with their cheque books and ordered Sundstrand's APS3200 to replace the AllliedSignal APU. These included Air France, Air Inter, All Nippon, Dragonair, Egyptair, Lufthansa and United Airlines. The advent of the 131-9(A) has helped stem the flow and recent victories chalked up by AlliedSignal include Aer Lingus, Leisure International, Syrian Arab Airlines, Monarch, China Eastern Airlines and GE Capital.
The biggest single order came in mid-1998 with the selection of the 131-9 by LanChile,the TACA group of El Salvador and TAM of Brazil as part of a wider equipment dealworth more than $100 million to AlliedSignal.
The regional market for aircraft of around 100 seats and fewer is also beginning to see increased activity as programmes firm up and, in the case of the 717-200, enter flight test. Sundstrand's APS2100 forms the vanguard of its attack on this market, having been selected for the 717. The engine is performing well in tests to date and is due to enter service with the launch customer AirTran in mid-1999. Like Boeing, Sundstrand is hopeful that the stagnant 717 orderbook will soon show signs of new life, particularly since the A318 (the Airbus rival to the 717, with a 131-9 APU), is close to launch after attracting the interest of International Lease Finance (ILFC).
More work on the 717 is particularly vital for Sundstrand, which was denied a place on Fairchild Aerospace's new family of regional jets by the AlliedSignal-led RE220. Designated the RE220FD, the APU is aimed initially at the 728JET, which is tentatively scheduled for certification around 2001. The RE220, developed with Italy's Alfa Romeo Avio, Germany's BMW Rolls-Royce, Japan's Kawasaki Heavy Industries and Singapore Precision Technologies, was developed for Bombardier's Global Express and Gulfstream GV business jets, though it has also been selected for the Canadair Regional Jet.
The APU is also considered a prime candidate for Bombardier's proposed BRJ-X regional jet family, although Sundstrand is expected to compete strongly. In terms of new regional jets, Sundstrand's APS500 has been enjoying the fastest build-up in deliveries on Embraer's RJ-145. Certificated in 1996, production of this robust APU will continue to be accelerated throughout 1999 to keep pace with the expanding ERJ-135/145 production line in Brazil.
Another new APU development expected to reach a peak in the first few months of 1999 is the development of the AlliedSignal 331-400B for the Boeing 767-400ER. The company stepped up work on the new APU in February 1998 after receiving a letter of authorisation from Boeing to proceed with development. The 331-400B is a derivative of the 331-350 which has more than 650,000h in service on the Airbus A330 and A340. Although the -400B uses the same power section as the -350, it has been redesigned with a new load compressor, gearbox and control system. Elements of these new features are derived from both the 331-500B designed for the 777, and from the 131-9 family. The first test engine is running and the company hopes to obtain US Federal Aviation Administration certification in May 1999.
Using techniques perfected on the 777 APU design, the 331-400 will be qualified for extended range twin operations and will be able to start and operate at up to 43,200ft (13,000m).
While AlliedSignal works on the 331-400, it is careful not to take its eye away from Airbus' plans for the A3XX or from Boeing's 747-X developments. Although it has reportedly discussed novel "twin-barrel" concepts (such as two 331 series APUs in tandem), the manufacturer is likely to consider all new designs when facing competition from Pratt & Whitney Canada.
The largest APU in production remains P&WC's PW901A developed exclusively for the 747-400. Although it is the only APU now made by P&WC, the company is expected to bid for the 747-X and the A3XX, possibly as part of an international team. With major developments expected for the 50 to 500-plus seat range, 1999 is expected to bring the 20th century to a lively end for APU manufacturers.
Source: Flight International
