What happened
On March 28, 2016, at 05:35 UTC, an air traffic controller at Szczecin-Goleniów Airport (EPSC) received a report from the crew of a Boeing 737-800 operated by Ryanair regarding a malfunction of the Precision Approach Path Indicator (PAPI) lights for Runway 31. The aircraft was conducting an approach from Oslo-Ryggae and was approximately 16 km from the runway threshold when the crew noted that the PAPI indications were inconsistent with the ILS signal, suggesting a glide path higher than the actual path.
At the time of the incident, meteorological conditions included high-level Cirrus clouds (3/8 coverage) and visibility exceeding 10 km.
The investigation
The investigation examined the PAPI units and the history of similar reports. It was established that between August 15, 2015, and March 28, 2016, there had been various reports of similar PAPI malfunctions on Runway 31. The investigation included a comprehensive technical inspection of the light units, covering factory seals, internal and external optics, light source functionality, reflectors, heating elements, electrical connections, and structural supports. Additionally, the angular settings of the units in both the horizontal plane and relative to the runway axis were verified, along with the stability of the foundations and the validity of the device certificates.
Findings
- The probable cause of the incorrect PAPI indications was condensation and frosting on the light units.
- Previous reports of similar malfunctions had been documented over the preceding seven months.
Safety action
Following the investigation, the PAPI system was temporarily deactivated. The airport management implemented an operational risk assessment and an optimistic recovery program, which included monitoring reports until a successful flight inspection could be performed. To prevent recurrence, the heating elements within the light units were upgraded to larger heaters to better combat moisture buildup. Furthermore, the light units are now inspected several times daily, and operators at EPSC are informed of the specific alignment parameters for the Runway 31 PAPI.