Introduction
On 31 March 2003 at 2338 UTC, an Airbus A320-231, registration G-MEDA, was on approach to Runway 25L at Addis Ababa Airport, Ethiopia, when a serious incident occurred. The investigation was the responsibility of the Ethiopian Civil Aviation Authority (CAA). The UK Air Accidents Investigation Branch (AAIB) published the results of their own investigation on the AAIB website in January 2008, including six draft Safety Recommendations, with the expectation that the Ethiopian CAA would include them in their official report. As of the AAIB Bulletin 6/2010, the Ethiopian CAA final report had not been published, and no timescales had been given. Therefore, the AAIB formally issued these six Safety Recommendations.
Safety Deficiencies
The systems fitted to the aircraft to provide a safety net against a Controlled Flight Into Terrain (CFIT) accident performed as designed but were ineffective in preventing the incident. Consequently, the safety of the aircraft during the ADS2 VOR/DME approach procedure was entirely dependent on the correct operation of the ADS VOR and its monitoring systems. The AAIB noted that for as long as the ADS VOR continued to radiate incorrect bearing information, there was a risk that another aircraft could suffer the same problem.
Safety Recommendations
Six Safety Recommendations were issued:
- Safety Recommendation 2010-020: The Ethiopian Civil Aviation Authority should review the quality mechanisms that govern maintenance and monitoring of the ground station facilities to ensure correct procedures and parts are used.
- Safety Recommendation 2010-021: The Ethiopian Civil Aviation Authority should review procedures for issuing NOTAMs and other safety information to ensure a more robust process.
- Safety Recommendation 2010-022: The International Civil Aviation Organization should review methods by which the effectiveness of radio navigation aid ground station monitors are assured.
- Safety Recommendation 2010-023: The European Aviation Safety Agency (EASA) and the Federal Aviation Administration (FAA) should review and revise existing TAWS certification requirements to protect against common mode failures that could induce a CFIT accident. Minimum requirements for navigational accuracy of sources used for TAWS should be tightened, and these revised standards applied retrospectively.
- Safety Recommendation 2010-024: EASA and the FAA should study issues relating to the use of TAWS so that flight crews can be alerted when data source problems are identified by the system.
- Safety Recommendation 2010-025: EASA and the FAA should consider whether crews should be alerted when a Flight Management System (FMS) identifies a recurrent problem with a navigation aid, and whether subsequent use of that aid for position information is desirable.
The report noted that both the FMS and TAWS had sufficient information to identify a problem with the ADS VOR, but there was no mechanism to communicate this effectively to the crew.