Lufthansa A321 at Hamburg on Jul 23rd 2019, almost collision with sail plane, 46 feet vertical, 184 feet horizontal remaining
Last Update: October 23, 2020 / 18:37:44 GMT/Zulu time
Germany's BFU reported in their July bulletin that radar data of the A321 as well as FLARM data of the sail plane indicate the separation between the aircraft reduced to about 50 meters (160 feet) horizontal and 200 feet vertical, the Airbus was below the sail plane. The data auggest that the A321 actually passed below the sail plane flying in the same direction. The sail plane was on a VFR flight together with another sail plane. The pilot reported she was at about 3600 feet in a northwesterly heading when suddenly the A321 appeared below her at about the same heading, she estimated the A321 passed her in a vertical distance of about 20-30 meters (70-100 feet) and 60-80 meters (200-250 feet) horizontally. The second sail plane was about 1.5nm northwest of their position at that point.
The BFU reported both aircraft were operating in airspace class E in which both IFR and VFR traffic operate, IFR traffic is separated to IFR traffic, traffic information to VFR traffic is provided where possible.
On Oct 23rd 2020 the BFU released their final report in German only ((Editorial note: to serve the purpose of global prevention of the repeat of causes leading to an occurrence an additional timely release of all occurrence reports in the only world spanning aviation language English would be necessary, a German only release does not achieve this purpose as set by ICAO annex 13 and just forces many aviators to waste much more time and effort each in trying to understand the circumstances leading to the occurrence. Aviators operating internationally are required to read/speak English besides their local language, investigators need to be able to read/write/speak English to communicate with their counterparts all around the globe).
The investigation reported based on radar data assessment that the minimum separation had reduced to 46 feet vertical and 56 meters/184 feet horizontal and concluded the causes of the serious incident were:
- the Airbus was cleared to descend to an altitude below the protected airspace class C at the Hamburg Fuhlbüttel Airport
- the closing speed and the flight trajectory made it impossible to the Airbus crew to spot the sail plane
- The airbus approached the sail plane from behind in an area invisible to the pilot of the sail plane
- The application of the principle "See and Avoid" was not possible for both the Airbus and the Sailplane pilots.
- All available warning systems (TCAS, STCA, Radar) were ineffective because they did not work without transponder on board of the sail plane
- The widespread FLARM collision warning device in gliding is ineffective in relation to airliners and doesn't warn against them.
The BFU complained that two safety recommendations issued in 2017 had not yet been put into effect: a recommendation to lift the abstention from requirement to carry transponders for sail planes and a requirement to ATC to be able to handle traffic information for any aircraft operating in their air space as well as airborne and ground based warning systems (ACAS and STCA) to be able to warn of collisions.
The BFU analysed that two sailplanes bound for Lübeck Blankensee were in cruise flight in the airspace below Class C of Hamburg Fuhlsbüttel. While one of the sail planes remained about 1.5nm from the A321, the other one came close to the A321, which approached from behind the sail plane so that the pilot had no chance to detect the A321 and thus could not initiated an escape maneouver.
The A321 was operating in Class E airspace and, according to current legislation, should have avoided the sail plane according to "See and Avoid" principles. The A321 was flying at 225 KIAS descending towards the ILS runway 23 of Hamburg Airport, the pitch was about 3.6 degrees nose up and the aircraft was in a left turn at 25 degrees bank angle. While preparing the aircraft for landing the crew experiences increased work load like working checklists, aircraft configuration and preparations for landing. A continuous observation of the airspace around is nearly impossible in this phase. In addition instrument panels and relatively small windows limit the outside view. The sailplane was in an 11 o'clock position slightly below the A321, due to the pitch angle it is thus likely that the sight to the sail plane was blocked by the instruments. The sun was in the west slightly above the horizon, a limitation of the view by sun glare can not be ruled out.
Due to the lack of a transponder on board of the sail plane and thus lack of TCAS the crew could only use the "See and Avoid" principle and could not detect the risk of collision in time.
The controller in charge of the Airbus was in compliance with the rules of the air traffic control company. He cleared the A321 to descend below Class C early in consideration to distribute the load on the frequency. However, the BFU annotated, the reduction of load on frequency could also have been achieved by using the standard approach procedures, which would have left the Airbus in the protected Class C airspace at all times. This would have been a safe operation even though it may have taken longer.
The controller's decision to guide an IFR flight through an airspace, in which unknown and not radar/TCAS detectable traffic can legally operate, without compelling necessity can not be understood by the BFU. As long as it is permitted to operate in Class E without active transponder or other radar and TCAS compliant equipment, this should be absolutely avoided to reduce the risk of collisions, traffic acceleration must not be prioritized.
This article is published under license from Avherald.com. © of text by Avherald.com.
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