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| Date: | Monday 15 April 2024 |
| Time: | 09:27 |
| Type: |  Boeing 737-9KVER (WL) |
| Owner/operator: | Windrose Airlines |
| Registration: | UR-PSI |
| MSN: | 41534/4524 |
| Year of manufacture: | 2013 |
| Engine model: | CFMI CFM56-7B |
| Fatalities: | Fatalities: 0 / Occupants: |
| Other fatalities: | 0 |
| Aircraft damage: | None |
| Category: | Incident |
| Location: | E of Felixstowe, East Suffolk, Suffolk -
 United Kingdom
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | Chisinau Airport (KIV/LUKK) |
| London-Luton Airport (LTN/EGGW) | |
| Investigating agency: | NBAAI |
| Confidence Rating: |  Accident investigation report completed and information captured |
Flyone flight 5F617, a Boeing 737-9KVER operated by Windrose Airlines, was descending through an altitude of 16,550 feet when, before entering the clouds, in accordance with the OM, the crew turned on the engine anti-icing system "ENG 1&2 ANTI-ICE" and continued the descent. While crossing FL150, the crew detected significant icing on the aircraft, accompanied by ice accumulation on the windshield and wipers. At 08:30, at an altitude of 14,000 feet, the crew turned on the wing anti-icing system "WING ANTI-ICE." At the same time, moderate turbulence was felt. The speed indicators of the PIC and the co-pilot displayed a light warning about the difference in indicated airspeed values (IAS DISAGREE), and a speed drop was observed on the PIC display. The crew performed the airspeed unreliable non-normal checklist procedures using the auxiliary display for speed indication, continued the descent, and declared a "MAYDAY" distress signal. At 08:46, after exiting the clouds at an altitude of 4,835 feet, the speed indicators on the PIC display normalized, after which the PIC engaged autopilot "B" and canceled the "MAYDAY" call. The landing was successfully performed on runway 25.
During the post-flight inspection, no deviations in the aircraft's systems were found, and a decision was made to perform the return flight on the London-Chisinau route, which was completed without remarks.
As a result of a detailed fault search at the Chisinau Airport, the airline's engineering team found a significant decrease in resistance (down to 16 Ohms) between contact 41 (pin41) of connector D644 of the dynamic air pressure receiver (LH Pitot Probe) and "ground," which is below the established limit of 40-56 Ohms. It is likely that during the aircraft's stay in the heavy icing zone, the low resistance resulted in insufficient current flow for proper heating of the dynamic air pressure receiver, causing ice accumulation on the LH Pitot Probe. After replacing the LH Pitot Probe, the aircraft was cleared for further operation without restrictions.
Sources:
NBAAI
https://nbaai.gov.ua/wp-content/uploads/2024/05/04_apr_24.pdf
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 24-May-2024 18:28 | ASN | Added |
| 24-May-2024 18:29 | ASN | Updated [Departure airport, Damage, ] |
| 14-Dec-2024 07:43 | Anon. | Updated [Location, Departure airport, ] |
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