Guy Norris/SEATTLE
The aviation industry's continual search for safer skies is reaching "crusade" status as the chilling implications sink in of predicted traffic growth on accident rates. The US Federal Aviation Administration, for example, expects "a serious accident" every week by 2015 unless some radical changes are made. That prediction is based on the 1996 accident rate of one-per-million departures.
Pierre Jeanniot, director general of the International Air Transport Association (IATA), bluntly states: "If we do not reduce the current accident rate, then at a future time when there is twice as much traffic, we will have twice as many accidents." IATA has set itself the target of developing a strategy to reduce the aircraft hull loss rate by 50% by 2004, and is among several organisations, airlines and manufacturers which have begun to raise awareness of the potential dangers ahead.
One company, AlliedSignal in the USA, believes that its broad range of safety-related avionics gives it "-an obligation to look at ways of enhancing safety", says Frank Daly, vice-president and general manager of the Redmond, Washington-based Air Transport and Regional Avionics division. The company is aiming for an "integrated hazard avoidance system [IHAS]" which combines its enhanced ground proximity warning (EGPWS), multi-function radar and traffic alert and collision avoidance systems (TCAS).
Unlike navigation systems, which are now being integrated on a wider scale than before, safety-related avionics have deliberately remained discrete. Although this is partly because of their development as separate systems, it also owes much to the sensitivity with which they are viewed by airlines, manufacturers and regulatory authorities. "IHAS requires the co-operation of the airframers, but even then it will be difficult," says Daly. "It requires a profound change in thinking on all sides. We are, however, meeting with some success with Airbus and Boeing, both of which are keeping the doors open."
The idea is simple. The next generation of airliners, like Airbus' proposed A3XX, could be equipped with totally integrated safety systems that will merge data from all sensors to give the crew an instant, clear, hazard warning. "It offers obvious benefits in terms of cost, weight and power [such as sharing processing power between TCAS/EGPWS], but it also has less obvious benefits. If the radar knows what the EGPWS and TCAS know, then rather than barrage the crew with different sets of data, we would just merge it together," says Daly.
"It's a case of one plus one equals three when they start to work together," says Daly, who describes the IHAS concept as a "more holistic" approach to safety.
AlliedSignal's provisional road map to IHAS shows development as early as 2001. Further down the road, by around 2003-4, IHAS is also expected to feed into a fully fledged enhanced situational awareness system (ESAS), which would include inputs from new sensors linked to a head-up display.
A3XX CONTENDER
Airbus is discussing the potential development of IHAS for the A3XX with AlliedSignal, although "-we haven't reached an agreement", he adds. Airbus has been "encouraging" about the concept, which will employ upgraded algorithms, such as TCAS, in each subsystem.
"We want to be able to take it to the next level and produce something we call 'smart alerting'," Daly says. The system will probably be designed around three main processors for high levels of redundancy. "If one goes out, we want it to gracefully. If two go out, we'd still have full capability. We will guarantee that, in the worst of all cases, it will degrade to today's standard," he says.
Development is not formally launched, but AlliedSignal has a design team working on IHAS and plans to "-send a large contingent" to Airbus in early September. To do business with Airbus, Daly expects that "-we would have to have a European partner".
The company believes it can sell IHAS to Airbus on its technological merits, arguing that developments have reached a plateau in most other areas of subsonic aircraft activity. "It is the area that offers the most opportunity for breakthroughs because the consumer computer business is continually driving new advances," comments Daly.
EGPWS PROGRESS
Building blocks for IHAS, meanwhile, are reaching an advanced stage. The EGPWS is entering service rapidly, with more than 360 aircraft equipped by the start of August, the bulk of which were linked with flight management/ inertial navigation systems rather than global positioning systems (GPS).
More than 750,000 flight hours have been amassed, with the level of all nuisance alerts down to less than one in 26,000h. The introduction of software and database amendments are expected to reduce this to less than one nuisance alert in 100,000h.
Certifications are also rolling through at a rapid pace, from the Airbus A319/A320/A321 last September, through the Boeing 777-200/300 earlier this year, to the Next Generation 737, 747-400, 757 and 767-200/300 in January 1999 and 767-400 in April 2000. Airbus plans to certificate the A330/A340 with the EGPWS in November, while Boeing planned to clear the system on the MD-11 by August, the MD-10 in December and the 717 in April 1999.
Supplemental type certificates for in-service aircraft have been accumulated through airline customers covering the Airbus A300-600, Boeing 737, 757, 767, MD-80 and Fokker 100, with the A310, 727-200, 737 "Classics", DC-8, DC-9, DC-10 and MD-88/90 planned for this year and next.
The EGPWS takes the traditional Sundstrand-developed GPWS one step further by including a terrain database to provide much earlier warning to the crew when approaching high ground. AlliedSignal developed the added feature to overcome significant weaknesses in the existing system, which relies on a radio altimeter to detect rising ground.
Data indicate that, of all commercial jet accidents involving controlled flight into terrain (CFIT) between 1988 and 1995, 31% had no GPWS installed. Of the remainder, 28% were configured for landing and therefore had no warning, while the rest were caused by late warning or an improper pilot response.
Business is brisk and will get busier with an impending US Federal Aviation Administration ruling that, from 2000, all US-registered new-production aircraft with six seats and above be equipped with the EGPWS. All in-service aircraft will have to be retrofitted by 2003. "Next year we'll build about 6,000 units," says GPWS products director Brian Pulk, who estimates a market for around 25,000 systems in total. "Building them isn't the main issue, its getting them certified and installed."
Integrating the EGPWS with other safety systems has already begun. AlliedSignal and Boeing recently completed an 18-month programme which linked the EGPWS with the forward-looking windshear detection radar. The feature prioritises the most important warnings first and allows multiple hazard conditions to be flagged up in an orderly manner. "We use the EGPWS as an arbiter-it will be introduced on all the new Boeing types as they certify the EGPWS and weather radar with windshear warning," says Pulk. The prioritisation puts "rocks and weather" first. This assumes a CFIT or windshear situation is at hand and needs to be addressed before other alerts such as TCAS.
EGPWS improvements include the introduction of a "peaks" mode, developed at the request of British Airways. Normally, the display would be blank if there was no terrain within 2,000ft (600m). In peaks mode, however, the system provides a terrain display during cruise to improve situational awareness.
BA intends to use the system on routes over mountain ranges such as the Himalayas. By knowing what the terrain below is like at all times, crews will be able to execute more rapid descents in case of a depressurisation, or other emergency. This means less oxygen is required, freeing up extra payload or fuel capacity.
AlliedSignal is testing a new algorithm to calculate the aircraft's true altitude, using static pressure, air temperature, GPS and radio altitude, EGPWS data and corrected barometric altitude. It hopes that the new method will eliminate errors introduced by the present system, which is based on corrected (or converted) barometric altitude.
Perhaps the most interesting moves towards IHAS are the links being developed between the company's RDR-4B X-band weather radar, the EGPWS and TCAS. "We intend to develop our current radar, which can detect windshear at low altitudes, into a system that can also be used at altitude for clear-air turbulence [CAT] detection," says radar and TCAS chief engineer Daryal Kuntman.
It is possible to convert the RDR-4B into a multimode radar because of advances in signal processing and links to the other safety systems, Kuntman says. "In the past, both the -4A and -4B had limited turbulence detection capability, but they weren't very successful because there was no sophisticated signal processing capability. We had limited clutter filtering so it was susceptible to false alarms." The radar's low pulse-repetition frequency is being raised to increase signal gain and give more effective filtering.
Data will be collected this year on the company's Convair 580 testbed during flights in Alaska. New algorithms will be tested in the second quarter of 1999, with certification targeted for early 2000. The company believes the radar's predictive windshear capability, which relies on Doppler returns from airborne moisture, will be adequate for forecasting turbulence at higher altitudes. Data suggest that many of the most severe CAT events are not "dry", and have moisture associated with them. An on-board infrared radiometer is still being considered for a full-up ESAS suite.
Using the terrain and altitude information available from the EGPWS, AlliedSignal plans to determine the optimum tilt angle for the radar to maintain a consistent level of ground clutter on the display. In addition, a vertical profile display is planned which would present combined radar and EGPWS hazard information in the vertical plane along the flightpath. The incorporation of TCAS data is also being considered, to provide a concrete stepping stone to the full implementation of an IHAS.
Another combined use being planned is terrain data correlation. By correlating radar ground-mapping data with the EGPWS terrain database, the system will be able to verify the integrity of navigation data entering the EGPWS and detect potential database errors. This feature can also provide an alert for obstacles that are not in the database.
TCAS to ACAS
The third major element of AlliedSignal's IHAS pyramid is its TCAS 2, which is to be renamed ACAS II in recognition of the international airborne collision avoidance system requirement. The move is also a marketing ploy in the tough TCAS arena where the company competes with Honeywell and Rockwell Collins.
The FAA successfully completed flight trials of the latest TCAS Change 7 software in July and expects certification later this year. Change 7 enhances the abilities of the TCAS to filter resolution advisories, incorporates more stringent criteria for removing traffic advisories and improves surveillance in high-density traffic areas. The latest TCAS software standard forms the basis for the ACAS II requirements which come into effect in Europe from 1 January, 2000. Many European carriers have yet to decide on a choice of equipment.
AlliedSignal's future direction with the ACAS is tied closely to development of the automatic dependent surveillance - broadcast (ADS-B) system. ADS-B is being pushed as a low-cost alternative with many of the features planned for IHAS, but by incorporating the longer detection range capability of ADS-B into its future TCAS/ACAS solution, AlliedSignal hopes to capitalise on both.
"Extended range will happen. We still believe the real big jump will be when ADS-B gets implemented. It will be a quantum jump," says Kuntman, who expects the resulting involvement of the GPS to be "the key". The combination of ADS-B's passive surveillance capability - out to 180km (100nm) - with TCAS active surveillance is "-being considered the next generation improvement", he adds.
Source: Flight International
