Air Transportation Safety Information Letter A21O0066-D1-L1

09 March 2022

Director General, Civil Aviation
Transport Canada

On 06 August 2021, the Beechcraft King Air A100 aircraft (registration C-GKAJ, serial number B232) commercially registered to Thunder Airlines Limited (Thunder Airlines) was conducting scheduled flight THU107 from Timmins (Victor M. Power) Airport (CYTS), Ontario, to Moosonee Airport (CYMO), Ontario, with 2 crew members and 7 passengers on board. 

At the time of the occurrence, there was heavy rain in the vicinity of CYMO. The aircraft conducted a first approach to Runway 06, unsuccessfully. This was followed by a second approach, this time for Runway 24. While on short final, the crew was able to acquire the required visual references to continue the approach to land. After touching down at approximately the midpoint of Runway 24, the aircraft continued along the runway, overran it, and came to a stop approximately 50 feet beyond the end of the runway. There were no injuries and no damage to the aircraft.

The investigation has now concluded with the final report released on 11 February 2022.

During the designated reviewer process, it was brought to the TSB’s attention that approach procedures with vertical guidance (APVs) to aerodromes with shorter runways may not be harmonized with the visual approach slope indicator systems (VASIS). Published APV approaches, such as lateral navigation/vertical navigation (LNAV/VNAV) or localizer performance with vertical guidance (LPV) approaches, are typically designed for a threshold crossing height at 50 feet above ground, which will allow the aircraft to be guided to a touchdown point approximately 1000 feet down the runway.

VASIS is a generic term referring to VASI (visual approach slope indicator), AVASI (abbreviated VASI), PAPI (precision approach path indicator), and APAPI (abbreviated PAPI). One or more of these types of systems are installed at many aerodromes across Canada. Although not a factor in this occurrence, runways 06 and 24 at CYMO had APAPIs installed; however, these systems were both reported by NOTAM as being unserviceable at the time of the occurrence.

When VASIS are installed at aerodromes with shorter runways, the threshold crossing height could be much less than for a typical APV approach. When flight crews conduct an APV approach to minimums and then transition to visual references, they may see conflicting information between the VASIS indication and the APV approach slope: they may see for example an above slope indication (all white lights), which would translate to being too high on the visual approach slope for landing. This discrepancy between the VASIS indication and the APV approach slope may lead the flight crews to increase the descent rate, potentially leading to an unstable approach.

The Transport Canada Aeronautical Information Manual states the following:

Where a PAPI or VASI is provided on a precision or non-precision approach runway and has not been harmonized with a vertical guidance signal, it will be turned off in weather conditions involving a ceiling of less than 500 ft (150 m) and/or visibility less than 1 mi., unless specifically requested by the pilot. This is to avoid possible contradiction between the electronic precision or non-precision approach vertical guidance and visual (VASI/ PAPI) glide slope signal.^{Footnote 1}

NAV CANADA provides similar instructions to its flight service station (FSS) and tower personnel in its latest Manual of Air Traffic Services.^{Footnote 2} This procedure may benefit flight crews when either FSS or tower personnel have the ability to turn off the VASIS in the conditions described above. At aerodromes equipped with an aircraft radio control of aerodrome lighting (ARCAL) system, flight crews do not have the ability to turn off the VASIS to avoid possible contradiction between APV guidance and VASIS indications.

Transport Canada’s Advisory Circular (AC) 302-009, Precision Approach Path Indicator Harmonization with Instrument Landing System, also provides information on the installation of PAPI light units to enable harmonization of the PAPI signal with instrument landing system (ILS).

This Safety Information Letter is issued to bring to your attention the potential of contradictory cues that flight crews may receive when conducting APV approaches to aerodromes with shorter runways equipped with VASIS.

The foregoing is provided for whatever follow-up action is deemed appropriate. The TSB would appreciate being advised of any action that is taken in this regard.

Yours sincerely,

cc:

• President and CEO, NAV CANADA
• Director, Safety Policy and Intelligence – Civil Aviation, Transport Canada
• Minister’s Observer – Civil Aviation, Transport Canada
• President, Thunder Airlines
• Director of Flight Operations, Thunder Airlines