NZ 60 AT APIA
VIDEOS OF NZ 60
|(Video embedded from YouTube on 18 September 2010)|
|(Video embedded from YouTube on 18 September 2010)|
|(Video embedded from YouTube on 18 september 2010)|
On the 30th of July 2000, a New Zealand B767 jet bound for Faleolo International Airport, Apia encountered an erroneous ILS indication on approach. There were airfield works in progress at the airfield. There were 9 NOTAMS issued on the serviceability of the various navaids at the airport.
The crew briefed for an ILS approach with the VOR approach as a backup. The flight was cleared for the FALE arrival 15 mile ARC for ILS 08. A low drag approach was conducted with a tailwind of 10 knots.The Localiser was captured at 14 nm with FLAP 1 and 220 knots. One second after the APPROACH mode was armed, the glideslope was captured by the autoflight system. The indications showed the aircraft at the correct flight profile without any warning flags with the ident of the ILS being emitted.
On capturing the glideslope, the aircraft pitched down lower than usual with an increase in airspeed and higher rate of descend. The crew proceeded to concentrate on the management of the energy of the aircraft with the use of speedbrake, gear and flaps.
After landing flaps were selected, the Pilot Flying noticed the anomaly of DME vs altitude. The Pilot Monitoring noticed that the visual cues (the proximity of the island light looked closer) did not correspond to his mental picture.
A go around was called by all pilots and executed at 6 nm from the runway threshold. A second approach was conducted as a Localicer approach disregarding the glideslope signal.
The NOTAM issued by the authorities labelled the Glide Path as “unmonitored”. The crew were not aware of the significance and meaning of the terminology.
- The ILS installation was allowed to radiate the Glide Path signal in the bypass mode with the unserviceable transmitter selected.
- The ident of ILS is only carried on the Localiser only and not the Glide Path. Therefore a working doesn’t assure the integrity if the Glide Path as initial assumed by the crew.
- The normal mindset is to trust the most accurate navaid, in this case the ILS.
- The assumption that the higher rate of descend was due to the tailwind and not the erroneous signal.
- The absence of any warning flags to give the crew indications of an erroneous signal.
- The industry wide lack of awareness of the phenomenon of erroneous transmissions.
- The clearing of the aircraft and crew by ATC for the Full ILS approach
THE INCIDENT EXPLAINED USING REASONS SWISS CHEESE MODEL:
Using Reasons swiss chees model we can see how the different barriers were penetrated:
- The first defence was breached with the unfamiliarity of the NOTAM terminology.
- The second defence was breached with the monitored ident which gave the crew a false sense of belief that the glide path was functioning.
- The third defence was breached with the absence of any warning indications or flags in the flight deck to alert the crew of an erroneous glide path.
- The fourth defence was breached when the glideslope height check was not completed.
- The fifth defence was breached when the aircraft’s GPWS warning remained silent as the aircraft was correctly configured for landing and all the GPWS system requirements were met.
- The sixth defence held – Situational Awareness of the crew. This was activated by the glideslope capture unease, increased workload, proximity of the island lights and the conflict between the DME/Altitude check.
MITIGATING FACTORS FOR NZ 60:
The factors that mitigated this flight from becoming an incident were:
- CRM displayed by all the crewmembers onboard.
- The Approach briefing was through and planned carefully. The alternate briefing of the use of VOR approach as a contingency showed forward planning. This allowed all crewmembers to share the same mental model.
- There was continuous questioning of the state of the aircraft leading to the DME/Altitude check discrepancy.
- The use of external visual aids (island lights) to increase situational awareness.
- The correct decision to conduct a Go Around.
- The use of automation to reduce workload.
- The open communication and teamwork displayed.
- The decision to conduct a Localiser only approach on the second approach.
OTHER FACTORS THAT CAN BE USED TO MITIGATE AN ERRONEOUS/FALSE ILS :
The other methods that can be used to identify an erroneous / false ILS are:
- Have awareness of the possibility of erroneous indications, including the non appearance of warning flags. Forewarned is forearmed.
- Diligently check and understand the terminology of NOTAMS to determine the operational status of the ILS
- Do a through briefing - including all the pertinent points such as MSA, location of terrain, man made objects, vertical speed expected and groundspeed expected to have a mental model of the approach.
- Conduct a stabilised approach. This would allow for a reduction of workload freeing up additional mental capacity to identify anomalies.
- Maintain situational awareness throughout the approach. Constantly questioning if the indications show on the instruments are correct.
- Be alert when conducting approaches into uncontrolled airports where the ILS area is not protected by ATC. In airports such as these, there lies the possibility of interference with the ILS signal and erroneous signals.
- Do a crosscheck of the altimeter against the published glideslope crossing altitude at the FAF, followed by continuous distance and height check for verification of the correct profile flown
- Use raw data sources as a measure of crosschecking that the aircraft is on the correct Localiser course – Usage of markers or co sited VOR
- Query ATC if in doubt of the status of the ILS or Approach clearance. This is a measure of cross checking to ensure that the correct approach has been assigned
- If in doubt and faced with indications that are contrary – if not visual with the runway, conduct a Go AROUND.