History
On 17 November 2003 at 18:36 UTC, GMI2139, a Fokker 100 operated by Germania, reported flight level 340 on frequency 124.030 MHz. The radar controller cleared it direct DITON at flight level 340, then instructed descent to flight level 320 at 18:47 and handed it over to Zurich sector U2.
At the same time, GNR310A, a Boeing 737-8 operated by Futura International Airways for Gambia International Airlines, reported flight level 360 on frequency 128.155 MHz. A trainee radar controller identified it, cleared it via LAMUR-DITON at flight level 360, and noted speed at the pilot's discretion. Oral coordination with sector MS4/MA4 planned descent to flight level 330.
At 18:49, the trainee instructed GNR310A to descend to flight level 300 (not 330) at 2000 ft/min or more. The pilot read back flight level 300 correctly but the rate readback was unclear. The controller did not correct it.
At 18:51:01, the STCA activated. GNR310A was at flight level 327 descending, and GMI2139 was at flight level 320. The controller then instructed immediate climb to flight level 330, which the pilot did, noting he had been cleared to 300. The controller did not dispute this. The minimum vertical distance was 100 ft with 4.2 NM lateral separation; later 700 ft at 3.7 NM.
Findings
- The incident occurred at 18:51:01, 15 NM SSW of KORED, in class C airspace at flight level 320.
- Instrument flight rules applied.
- GMI2139 was in contact with Zurich sector U2; GNR310A with Geneva sector MS5/MA5.
- The coach and coordinator held appropriate licences; the radar controller was in training.
- Both aircraft were on the same route (TDP-OMASI-LAMUR) with slightly converging headings.
- GMI2139 flew at 405 kt, GNR310A at 435 kt.
- The trainee cleared GNR310A to flight level 300 instead of 330; the pilot read back 300.
- Neither the coach nor the coordinator detected the error.
- The trainee entered flight level 330 on the control strip.
- Both aircraft had TCAS; GNR310A's commander later reported that TCAS never issued a TA or RA.
- GMI2139's commander did not notice anything.
- Weather conditions were reported.
Analysis
GMI2139 and GNR310A were flying the same route to Munich, parallel at 4 NM lateral and 2000 ft vertical separation. GNR310A was slightly behind and faster, gradually closing the gap. GMI2139 descended to flight level 320 at 18:47 and was handed off to Zurich. GNR310A at flight level 360 was cleared to flight level 300 instead of 330 after coordination with MS4/MA4. The trainee transmitted flight level 300 but entered 330 on the strip, unable to explain the discrepancy. The pilot's readback was correct for 300 but the rate unclear. Three controllers worked the sector; none noticed the error. The lack of headsets for the coach and coordinator may have been a factor.
At 18:51, STCA alerted; GNR310A was passing flight level 327, descending, while GMI2139 was at flight level 320. The controller ordered immediate climb to flight level 330, which the pilot did, stating he had been cleared to 300.
Cause
Issuing by the trainee radar controller of an incorrect flight level clearance, detected by neither the coach nor by the coordinator.
Factor affecting the evolution of the incident: The fact that the coach and the coordinator were not wearing headsets.