|Title:||Near-miss between a DHC-8-311, LN-WFR, and Boeing 737-800 (Recommended)|
|Micro summary:||A cascading series of errors results in a near-miss.|
|Event Time:||2004-11-29 at 1219 and 1223|
|Publishing Agency:||Accident Investigation Board Norway (AIB)|
|Site of event:||Bergen Flesland Airport, Norway (ENBR)|
|First Airplane||Second Airplane|
|Departure:||Sandefjord Airport, Torp, Norway||Larnaca International Airport, Larnaca, Cyprus|
|Destination:||Bergen Airport, Flesland, Bergen, Norway||Bergen Airport, Flesland, Bergen, Norway|
|Airplane Type(s):||Bombardier Aerospace||Boeing 737-800|
|Operator(s):||Wideroes Flyveselskap||Eurocypria Airlines|
|Type of flight:||Revenue||Charter|
|Executive Summary:||ECA978 was arriving ENBR from Larnaka International Airport, Cyprus (LCLK) on a non- scheduled flight and was cleared the Standard Instrument Arrival (STAR) SOXUS 1E and descent to 6 000 ft for a later ILS approach to runway 17. WIF408 was a scheduled airline flight from Sandefjord Torp Airport, Norway (ENTO) to ENBR. The air traffic controller at Flesland Approach (APP) evaluated the approach sequence and decided that WIF408 was number 1 for the approach. |
By mistake the air traffic controller cleared WIF408 direct to OKITO, a reporting point on extended centreline of RWY 35. This made WIF408 turn onto a southwesterly heading. When the air traffic controller observed the turn on the radar screen he corrected this by reclearing WIF408 direct INTEL, a point on the extended centreline of RWY 17. Sequencing was no longer favouring WIF408 due to the unintended delaying “dog leg” turn. The air traffic controller decided to keep the sequence with WIF408 as number 1 by giving WIF408 the opportunity to track direct to the field for a later visual approach. At 12:17:00 WIF408 was cleared by Flesland APP to fly heading 270° and to descend to altitude 5 000 ft, antisipating to get visual with the field in sight. Heading was adjusted to 280° one minute afterwards. Tracks of the aircraft are shown on a cut from the AIP Norway STAR Chart AD2 ENBR 4-18 in the Appendix (based on radar recording).
Both aircraft were descending when the air traffic controller of Flesland APP at 12:18:30 noticed that vertical separation between the two aircraft was decreasing. Their tracks were crossing east of ENBR and separation was based on minumum 1 000 ft difference in altitude observed by ATC radar from SSR-transponder altitude information read-out (Mode C). The radar display system, Norwegian Air Traffic Control System (NATCON), can show rate of climb/descent of aircraft on the radar label. This function of the radar display was not used during the incident.
The air traffic controller instructed at 12:18:45 WIF408 to increase descent rate. WIF408 did not respond to this transmission and the instruction was repeated. The flight crew then responded that they were unable to comply due to the fact that they were descending at idle power and maximum speed (IAS equal Vmo). The aircraft approached each other fast on crossing tracks and the air traffic controller instructed ECA978 to stop the descent. ECA978 complied and levelled off at FL83.
Instructions were not timely to avoid a loss of separation between the two aircraft. A radar recording from the Air Navigation Service Provider (ANSP), Avinor, shows that Mode C read-out was less than 1 000 ft during 30 seconds. Minimum vertical distance shown by Mode C was 700 ft while lateral separation was less than 5 NM, 1 NM at minimum. Both flight crew received Traffic Advisory from their TCAS. The radar display system of Flesland APP showed a Short Term Conflict Alert (STCA) warning on the labels of both aircraft for 1 minute.
After the two aircraft had passed each other WIF408 was still IMC and received a radar vector to heading 350° for a downwind for later visual approach. Weather conditions prevented the flight crew of WIF408 from getting the field in sight. The air traffic controllers at TWR and APP had a short telephone coordination and decided that the weather no longer favoured visual approaches from the east. WIF408 received a descent clearance to 4 000 ft and a new vector to heading 020° in sequence behind ECA798 for the ILS-17.
At 12:23:00 WIF408 asked Flesland APP to confirm that an aircraft ahead was 4 NM away and descending to the same altitude. Flesland APP replied that radar showed 5 NM to the aircraft on base leg, descending through 3 600 ft for 3 000 ft. This was ECA978. A short discussion followed between WIF408 and Flesland APP on the radio frequency whether this was “the second airmiss with the same aircraft”. The flight crew of WIF408 stated that TCAS showed the aircraft ahead at a distance of 3 NM. The flight crew of ECA798 overheard the discussion and monitored WIF408 on their TCAS, but saw no reason to react to the situation.
Radar recording shows the two aircraft in sequence on downwind and base leg in a radar circuit for ILS-17. Minimum lateral distance was observed to be 4.6 NM by AIBN based on use of the Vector function on the radar display system (NATCON). Minimum vertical distance was 700 ft. Separation was lost during 30 seconds before vertical separation was re-established. AIBN has not found support for the flight crew claim of 3 NM minimum distance. The aircraft ahead was descending away from the altitude of WIF408.
|Learning Keywords:||Operations - Airspace - Air Proximity|
|Operations - Airspace - Air Traffic Control|
|Operations - Airspace - TCAS|
Accident Reports on DVD, Copyright © 2006 by Flight Simulation Systems, LLC. All Rights Reserved. All referenced trademarks are the property of their respective owners.www.fss.aero