In 1996, the United States (US) National Transportation Safety Board (NTSB), issued the following safety recommendation, A-96-101, that the US Federal Aviation Administration (FAA):
Examine the effectiveness of the enhanced GPWS, [Ground Proximity Warning System] and, if found effective, require all transport-category aircraft to be equipped with an enhanced GPWS that provides pilots with an early warning of terrain.
That recommendation was issued in response to several fatal, controlled flight into terrain (CFIT), accidents involving turbojet powered aircraft, including a Boeing 757 (757) on a flight from Miami, Florida to Cali, Columbia. While the installation of GPWS was not required for all turbojet powered aircraft at that time, the 757 was fitted with GPWS, but it had not provided sufficient warning for the flight crew to avoid collision with the terrain.
The system known as enhanced GPWS (also referred to as terrain awareness warning system-TAWS), includes a terrain database which, combined with navigation information, is able to provide a 60 second warning to the flight crew of potential CFIT. The system also has a terrain clearance floor function, which gives a warning if an aircraft descends prematurely during an approach to land. This provides protection from terrain and obstacles around airports and reduces nuisance warnings.
In response to the NTSB recommendation, the FAA commissioned a study by the Department of Transport Volpe Centre, which examined 44 CFIT accidents that occurred between 1985 and 1994 in the US to aircraft with six to 10 passenger seats. Of the 44 aircraft, 11 were powered by turbojets and 33 were powered by turboprops. None of the aircraft were fitted with a GPWS system. Computer modelling techniques used to analyse the data showed that had GPWS been fitted, 33 accidents could have been prevented; had enhanced GPWS been fitted, 42 accidents could have been prevented.
As a consequence of this study, the FAA issued a Notice of Proposed Rulemaking on 26 August 1996 and subsequently issued final rule 4910-13, effective on 29 March 2001. Rule 4910-13 required all turbine powered US registered aircraft manufactured after 29 March 2002, and configured with six or more passenger seats, to be fitted with an approved TAWS. Aircraft manufactured before this date were to be fitted with TAWS after 29 March 2005. Exceptions to this included parachute operations conducted within a 50 NM radius of the departure airport, fire fighting and aerial spraying operations.
Rule 4910-13 was incorporated into FAA Regulations Part 91, 121, 125, 129 and 135.
Subsequently, on 7 March 2006, in a synopsis of a report into a fatal accident involving a Sikorsky S-76A helicopter (NTSB report AAR-06-02), the NTSB advised that it proposed making the following recommendation to the US FAA as soon as possible:
Require all existing and new US registered turbine-powered rotorcraft certificated for six or more passenger seats to be equipped with a terrain awareness and warning system (A-06-XX)
International Standards
In 2001, the International Civil Aviation Organization (ICAO) reviewed Annex 6 to the Convention on International Civil Aviation, Parts I and II and subsequently amended the requirements for GPWS and TAWS on commercial and general aviation aircraft.
Section 6.9.2 of Annex 6 - Operation of Aircraft states that:
From 1 January 2007, all turbine-engined aeroplanes of a maximum certificated take-off mass in excess of 5,700kg or authorized to carry more than nine passengers, shall be equipped with a ground proximity warning system which has a forward looking terrain avoidance function.
Section 6.9.3 is a recommendation that states:
All turbine-engined aeroplanes of a maximum certificated take-off mass of 5,700kg or less and authorised to carry more than five but not more than nine passengers should be equipped with a ground proximity warning system which has a forward looking terrain avoidance function.
The European Joint Aviation Regulation, JAR-OPS 1.665, requires that any turbine powered aircraft with a maximum approved passenger seating configuration of more than nine, but not more than 30 must be equipped with TAWS. This regulation is effective from 1 January 2007 for aeroplanes certified before 1 January 2003 and only applies to commercial operations.
Transport Canada is proposing to amend its operating rules to be consistent with the FAA requirements.
The New Zealand Civil Aviation Authority, under Civil Aviation Rules (CAR) Part 125, requires air operator certificate (AOC), holders to ensure that instrument flight rules turbine-powered aircraft of less than 5,700 kg, with a passenger seating configuration of more than 5 seats, be equipped with a TAWS. CAR Part 125 will come into effect on 1 January 2007.
Australian Accidents
There have been a number of CFIT accidents in Australia, but within the last ten years the following occurrences are considered relevant:
ATSB occurrence 200105769:
On 10 December 2001, a Raytheon Beech 200C Super King Air was being operated under the instrument flight rules to Mt Gambier, S.A. At approximately 2333 Central Summer Time, the pilot reported to Air Traffic Services that he was in the circuit at Mt Gambier and would report after landing. At approximately 2336, the aircraft impacted the ground at a position 3.1 NM from the threshold of the runway. The pilot was fatally injured and the medical crew member sustained serious injuries.
ATSB occurrence 200302172:
On 15 May 2003, a Raytheon Beech 200C Super King Air was conducting an instrument approach to runway 21 at Coffs Harbour, N.S.W. The pilot conducted a missed approach from a low height and the aircraft impacted the sea, or a reef, approximately 3.2 NM north of the airport. During the missed approach the aircraft narrowly avoided a breakwater and an adjacent restaurant. During the subsequent landing the aircraft was substantially damaged.
ATSB occurrence 200402797:
On 28 July 2004, a Piper PA-31T Cheyenne with one pilot and 5 passengers, on a private, instrument flight rules, flight from Bankstown N.S.W, to Benalla, Victoria, collided with terrain 18 NM south-east of Benalla. All occupants were fatally injured and the aircraft was destroyed by impact forces and the post-impact fire. Instrument meteorological conditions existed at the time and the pilot had reported commencing a Global Positioning System, non-precision approach to Benalla.
ATSB occurrence 200102083:
On 27 April 2001, the crew of a Bell 407 helicopter was attempting to drop a liferaft, at night, to a sinking yacht on Howards Patch, Swains Reefs, Queensland. As the helicopter approached the yacht, the helicopter struck the water. The circumstances of the accident were consistent with controlled flight into the water at night. Both occupants survived the accident.
ATSB occurrence 200402038:
On 2 June 2004, an Australian registered Bell 212 helicopter impacted trees while manoeuvring in heavy rain during the approach to land at Same, Timor Leste. The helicopter was destroyed and three of the five occupants sustained serious injuries.
A full report of these accidents can be found on the ATSB website.
Australian legislation
The GPWS equipment required for Australian registered aircraft is detailed in the Civil Aviation Orders, which were amended on 28 January 2005.
The relevant section of Civil Aviation Order 20.18 para, 9.1C states that:
A turbine engined aeroplane that:
- has a maximum take-off weight of more than 15,000kg or is carrying 10 or more passengers; and is engaged in regular public transport, or charter, operations;
must not be operated under the Instrument Flight Rules unless it is fitted with:
- an approved ground proximity warning system (GPWS) that has a predictive terrain hazard warning function; or
- if paragraph 9.1CA applies - a GPWS that meets the requirements of section 108.361 (a section 108.36 GPWS); or
- if the aeroplane has a maximum take-off weight of 5,700 kg or less, but is carrying 10 or more passengers - a TAWS-B+ system2
A search of the CASA aircraft register database shows that there are more than 200 Australian registered turboprop aircraft with a seating capacity of less than 10. These aircraft are currently not required to have TAWS equipment as specified in the CAO.
ANALYSIS
There have been no reported CFIT accidents world wide involving aircraft that have been fitted with TAWS. The recommendations by ICAO and other accident investigation agencies have been made as a result of the availability of improved GPWS technology and CFIT being a significant factor in a number of aircraft accidents.
The accidents described above may not have occurred if ICAO recommendation 6.9.3 for the installation of TAWS in aircraft less than 5,700kg had been incorporated into the Australian Civil Aviation Orders. If the FAA requirements are adopted, the fitment of TAWS would be applicable to more than 200 aircraft currently on the Australian civil register, subject to seating configuration.
Further, if the NTSB proposed recommendation is adopted by the FAA in regard to helicopter requirements, this would be applicable to about 86 helicopters currently on the Australian civil register.
As a result of the above review, the Australian Transport Safety Bureau issues the following safety recommendation.
- Section 108.36 specifies a design standard for GPWS.
- TAWS B+ means a terrain awareness and warning system that is equipped with a visual display and complies with the requirements of Technical Standard Order C151.
