Mid-air separation between Boeing 737 and ultralight aircraft near Stuttgart

Casualties unknown • Stuttgart, DE

A Boeing 737-500 and a Comco Ikarus C42 experienced a close approach in Stuttgart airspace due to the ultralight aircraft operating at an unauthorized altitude.

What happened

On April 10, 2010, at approximately 18:00 local time, a mid-air separation occurred in the vicinity of Stuttgart Airport involving a Boeing 737-500 and a Comco Ikarus C42. The Boeing 737-500 was operating an IFR flight from Frankfurt to Stuttgart with 89 passengers. During the approach, the air traffic controller issued a traffic advisory to the crew, warning of VFR traffic at the two o'clock position. Simultaneously, the Boeing crew received a TCAS RA instructing them to adjust their vertical speed. Radar data confirmed that the minimum separation between the two aircraft was one nautical mile horizontally and 30 and 0 feet vertically.

The C42 was conducting a VFR flight from Friedrichshafen to Worms. While the aircraft was flying in Class C airspace, which extends from 3,500 ft to 5,500 ft MSL, the C42 was actually at an altitude of 4,500 ft. Upon noticing the Boeing 737 at their 12 o'clock position, the occupants of the C42 performed an emergency maneuver, applying heavy nose-down elevator and initiating a left turn. This maneuver caused the C42 to descend below 3,500 ft, exiting the Class C airspace.

The investigation

The BFU examined radar recordings from the air traffic service provider and radio communications between the controller and the Boeing crew. The investigation also reviewed the flight profile of the C42, including the GPS settings and the altitude settings used by the crew. The investigation established that the C42 was navigating via GPS, with a flight plan entered by the passenger that intended to keep the aircraft below 3,500 ft.

Findings

  • The C42 was flying at 4,500 ft MSL, which placed it within the controlled Class C airspace of Stuttgart, despite the flight plan intending to remain below 3,500 ft.
  • The pilot of the C42 did not realize the aircraft had entered the higher altitude stratum of the Class C airspace.
  • The C42 was operating at an unauthorized altitude due to a discrepancy between the intended flight plan and the actual flight level.
  • The passenger had set the altimeter to the QNH received in Friedrichshafen, and the pilot relied on GPS navigation for the route.

Probable cause

The primary cause of the separation was the C42 operating at 4,500 ft MSL, which placed it within the controlled Class C airspace, a deviation from the intended flight profile of staying below 3,500 ft.

Frequently asked questions

What happened in the 2010-04-10 1. Boeing Company B737-500 accident near Stuttgart, DE?

A Boeing 737-500 and a Comco Ikarus C42 experienced a close approach in Stuttgart airspace due to the ultralight aircraft operating at an unauthorized altitude.

What aircraft was involved and where did it happen?

The accident on 2010-04-10 involved a 1. Boeing Company B737-500, at Stuttgart, DE.

What was the probable cause of the accident?

The primary cause of the separation was the C42 operating at 4,500 ft MSL, which placed it within the controlled Class C airspace, a deviation from the intended flight profile of staying below 3,500 ft.

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