On 21 February 2001, a level bust 10 nm north of Oslo Airport in day VMC by a climbing PIA AIRBUS A-310 operating a scheduled passenger flight from Oslo to Copenhagen led to loss of separation with an SAS BOEING 737-600 inbound to Oslo from Alesund in which response to a co-ordinated TCAS RA by the A310 was not in accordance with its likely activation (descend). The B736 received and correctly actioned a Climb RA.
The following is extracted from the synopsis of the official AIBN (Norway) Report:
"SAS 2367 inbound to ENGM from Ålesund airport Vigra (ENAL), called Oslo ATCC Approach (APP) sector East at time 15:04:40, established on Standard Arrival Route (STAR) MES 2A arrival. The crew was cleared down to FL 100. PIA 752, flying from ENGM to Copenhagen airport Kastrup (EKCH), called APP sector East at 15:07:37 climbing to 7 000 ft on Standard Instrument Departure (SID) GOTUR 2A. PIA 752 was radar identified, and the crew was cleared climb to FL 090, and instructed to level off at FL 090 due to crossing traffic above (SAS 2367). The crew correctly read back the clearance to FL 090. At time 1509, both crew reported TCAS-alarm. At that time SAS 2367 was level at FL 100, and PIA 752 was approaching FL 090. The crew of PIA 752 did not stop their climb at FL 090, and as SAS 2367 passed just overhead the vertical distance had been reduced to 800 ft. The SAS 2367 crew had climbed to FL 102, according to TCAS Resolution Advisory (RA), and according to radar transcript, PIA 752 passed FL 094 and was still climbing. PIA 752 continued climb to FL 097, before staring descend back to FL 090. The horizontal distance though, had been increasing from the moment the vertical distance between the two aircraft was 800 ft."
The Report makes the following comments:
"It is the AAIB/Ns opinion that there was a risk of collision involved during this incident. The ATC planning was according to radar separation rules, but any traffic planning is depending on the involved aircrews acting according the instructions and clearances that has been issued. In this incident the crew of PIA 752 did not adhere to their clearance limit of FL 090, thus leading to a violation of separation minimums. Both crews reported TCAS warnings, and the SAS 2367 crew acted according to TCAS RA-climb. The PIA 752 crew also reported receiving RA-climb, but this seems inconsistent with how the ACAS system works, as the different TCAS installations are supposed to be ”communicating” in order not to create additional conflicts. According to radar transcripts, PIA 752 was observed in a steady climb to FL 094, and then a short halt followed by further climb to FL 097."