Assessment on evasive action near Muhos on July 20, 2024

The Safety Investigation Authority of Finland (SIAF) has completed an assessment1 on a hazardous situation which occurred near Muhos at approximately 2040 h on July 20, 2024, when a medical service helicopter conducted an immediate evasive maneuver.

FACTUAL INFORMATION
An EC142 helicopter operated by FinnHEMS departed the operator’s base at Oulu at 2030 h Finnish time on July 20, 2024, to respond to a traffic accident with a standard crew of a pilot, a helicopter emergency medical service crew member and a medical doctor on board. The pilot reported the departure on Oulu air traffic control (ATC) frequency. The helicopter proceeded toward Ristijärvi, climbing to 1,300 ft (approximately 400 m) altitude. The pilot set the radios to area control center (ACC) and Ahmosuo aerodrome frequencies.

When the helicopter was north of Muhos, the mission was changed. The new route took the helicopter in the direction of Kajaani, and therefore the pilot attempted to contact the ACC to activate a flight plan. The crew member was concentrated on his own duties, which left only the pilot responsible for visual scanning of the airspace. The pilot suddenly observed a light airplane closing on the helicopter from left and above. According to the pilot’s estimate, it was in descent and tracking approximately at right angles to the helicopter's heading. Estimated vertical separation was 100–300 ft2 and lateral separation was approximately 300 ft. The pilot stated that the airplane passed close enough to fill 70 % of the helicopter’s windshield. Earlier detection of the airplane had not been possible because the helicopter’s roof panel blocked a view to the left and up.

On seeing the airplane, the pilot called, “breaking left” and executed a violent evasive maneuver to low and left. At this point, the crew member also saw the airplane. The doctor, who occupied the rear seat, was talking on the phone, and was unaware of the airplane’s presence until he felt the helicopter enter the maneuver.

The pilot reported that the airplane was a high-wing light aircraft with a fixed landing gear, painted white with red cheatlines. The airplane was not in radio contact. Neither did it appear on the helicopter’s TAS3 display, which suggests that it was not equipped with a transponder4, or the transponder was switched off. The pilot assumed that the helicopter had not been spotted from the airplane since it closed on the helicopter from the sun, and during a left turn the helicopter was to the right of and below the airplane concealed behind its structure. The SIAF attempted to find the airplane’s pilot but was unsuccessful.

The pilot reported the occurrence to the ACC. The crew discussed the occurrence briefly and continued flight toward the Frontier Guard’s landing site in Kajaani, where the helicopter landed at 2112 h.

The crew conducted a defuzing session after landing. According to the pilot’s assessment, the crew was fit to resume the mission, which was duly completed. Next morning, the pilot contacted the FinnHEMS flight operations manager and prepared the required occurrence reports.

1 Safety Investigation Act 18§

2 100–300 ft equals approximately 30-90 m.

3 TAS = Traffic Advisory System that alerts the pilot of collision hazards.

4 A transponder automatically transmits a signal that creates a four-digit code on an ATC radar display. The controller can use the code to identify a particular aircraft.


Fig­ure 1. The tracks of the oc­cur­rence air­craft com­plete with time stamps. The he­li­copter's track is in blue, and the air­plane’s track is in red. Points A, B and C in­di­cate air­craft po­si­tions at the times given. (Fig­ure: Google Earth Im­age © 2024 CNES / Air­bus, an­no­ta­tions: SIAF)

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A side view of the crossing aircraft tracks projected on a Google Earth view. The track lines show the airplane approximately 100 ft above the helicopter. Times, aircraft speeds, and aircraft altitudes are also shown. The helicopter descends during the evasive maneuver.
Fig­ure 2. A side view of the cross­ing flight paths of the air­craft. The he­li­copter's track is in blue, and the air­plane’s track is in red. The air­plane has ap­prox­i­mately 100 ft ver­ti­cal sep­a­ra­tion to the he­li­copter un­til point B, where the he­li­copter per­forms a de­scend­ing eva­sive ma­neu­ver. (Fig­ure: Google Earth Im­age © 2024 CNES / Air­bus, an­no­ta­tions: SIAF)

BACKGROUND INFORMATION

Uncontrolled Airspace

Finland's national airspace is divided into controlled and uncontrolled airspace. Controlled airspace is an airspace of defined dimensions within which ATC services are provided. In an uncontrolled airspace no ATC services are provided. Aircraft positions are determined and aircraft are separated based on visual acquisition or traffic information transmitted by aircraft. A flight plan is not required for flight in an uncontrolled airspace, and aircraft are not subject to the same technical requirements as for flight in a controlled airspace (for example, a transponder is not mandatory).

Helicopter

The occurrence helicopter was an Eurocopter EC145 T2 manufactured by Airbus Helicopters. The medium-lift helicopter can carry up to 9 occupants and is certified for single-pilot or two-pilot operation. The occurrence helicopter was operated by a single pilot. The helicopter’s length is approximately 13 m and height approximately 3.5 m. The empty weight and maximum takeoff weight are 1,792 kg and 3,585 kg, respectively. Maximum speed is 268 km/h.

The helicopter is fitted with a TAS. The system derives information from mode C or S transponders of other aircraft and compares the altitude and track of these aircraft with those of ownship. If a collision hazard is developing, the system issues an alert. According to FinnHEMS procedures, a prescribed evasive action can be executed under visual flight rules conditions after an airborne target has also been acquired visually. However, the TAS will not detect aircraft that are not fitted with a transponder, or if the transponder is switched off.
The occurrence helicopter photographed from the right.
Fig­ure 1. The oc­cur­rence he­li­copter. (Fig­ure: Mika Laiho ©)

Meteorological Information

Weather was clear on a sunny summer evening. A meteorological aerodrome report (METAR) issued by the facility at Oulu reported CAVOK5. Weather was not a factor in the incident. However, it should be noted that at the time of the occurrence the sun was low and behind the helicopter, and therefore it is likely that the airplane pilot did not see the helicopter.

5 CAVOK = ceiling and visibility OK. The term indicates good flying weather, no cloud cover affecting flight, no significant weather conditions, and visibility more than 10 km.

FINDINGS
Because ATC services are not provided in an uncontrolled airspace, aircraft pilots will be responsible for visual scanning of airspace and transmitting traffic information. A TAS will not issue an alert of a closing aircraft if the transponder is switched off or is not fitted.

The SIAF will not initiate an investigation into the occurrence.

Further information:
Chief Air Safety Investigator Janne Kotiranta, tel. +358 2951 50703

Published 16.10.2024