Westjet B738 at Sint Maarten on Mar 7th 2017, go around on short final

Last Update: June 4, 2018 / 16:00:25 GMT/Zulu time

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Incident Facts

Date of incident
Mar 7, 2017

Classification
Incident

Airline
Westjet Airlines

Flight number
WS-2652

Departure
Toronto, Canada

Destination
Sint Maarten, Sint Maarten

Aircraft Registration
C-GWSV

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

Airport
Princess Juliana International Airport, Saint Martin

Airport ICAO Code
TNCM

A Westjet Boeing 737-800, registration C-GWSV performing flight WS-2652 from Toronto,ON (Canada) to Sint Maarten (Sint Maarten) with 164 people on board, had acquired visual contact with the runway 10 and was flying visually on very short final to Sint Maarten's runway 10 at about 15:33L (19:33Z), when the aircraft went around from low height, climbed to 4000 feet and entered a hold. The aircraft landed safely on runway 10 about 40 minutes after the go-around.

A ground observer had taken photos of the aircraft and published a story on Mar 9th 2017 claiming the aircraft nearly crashed into the waters at Sint Maarten but Westjet denying that there had been a close call.

On Mar 14th 2017 the airline released following statement quoted in its main part: "Video and photos of the missed approach spawned articles with unfortunate and frankly, irresponsible headlines such as, “Near Miss” and “WestJet denies close call caught on camera at St. Maarten,” with some even speculating on a potential disaster that was averted. We think it’s important to share with you what a missed approach means and how this “near miss” was anything but. Every day our pilots safely land some 700 flights throughout our network of more than 100 destinations in over 20 different countries, many of which have unique weather and terrain. Occasionally a landing will be aborted and a missed approach initiated if the pilots determine it’s the best option. In this case, our crew experienced rapidly changing weather conditions and as a result descended below the normal glide path on the approach to the landing. The crew recognized the situation, and the regularly trained and desired outcome was obtained – a safe missed approach to a safe landing."

According to position data and barometric altitude data (always using a standard pressure setting 1013hPa) received from the aircraft's transponder the aircraft was 0.57nm before the runway threshold at 0 feet when the aircraft initiated a go around, the rate of descent was just reducing but still indicating a descent and turning into a rate of climb. Corrected for the present ambient pressure 1019 hPa at the time of the short final the aircraft thus was between 157 (2.04 degrees glidepath) and 182 feet MSL (2.37 degrees glidepath) the transponder resolves the barometric altitude in 25 feet steps). In order to maintain a 3 degrees glideslope at that point the aircraft should have been at 230 feet MSL.

On Mar 17th 2017 the Canadian TSB reported: "During the approach to Runway 10 at TNCM, the aircraft descended too low on final and the flight crew executed a missed approach. A second approach was conducted and the aircraft landed without further event." The TSB rated the occurrence a "non-reportable incident" (an incident that is not required to be reported to the TSB) and opened a class 3 investigation (the reason for which could be amongst others: "there is significant public expectation that the TSB should independently make findings as to cause(s) and contributing factors").

On Oct 5th 2017 the TSB changed the occurrence classification from "non-reportable incident" to "incident reportable".

Runway 10 at Sint Maarten has 3 degree PAPI's left and right of the runway as shown by a current LIDO RNAV (GNSS) runway 10 approach plate (however, not on the aerodrome chart). In either case (157 to 182 feet) the flight crew would have seen 4 reds from the PAPIs (4 reds at 2.5 degrees or below). Pilots used to describe the PAPIs as "next to useless", there was also a discussion whether the PAPIs had been "retired".

On Jun 4th 2018 the Canadian TSB released their final report releasing following findings:

Findings as to causes and contributing factors

1. Significant changes in visibility were not communicated to the crew, which allowed them to continue the approach when the visibility was below the minimum required to do so.

2. The reduction in the pitch attitude led to an increase in airspeed, which resulted in a reduction in engine thrust and a higher rate of descent than that required by the 3° angle of descent.

3. The occurrence of a moderate to heavy rain shower, after the aircraft crossed the missed approach point, led to a significant reduction in visibility. The low-intensity setting of the runway lights and precision approach path indicator lights limited the visual references that were available to the crew to properly identify the runway.

4. The features of a hotel located to the left of the runway, such as its colour, shape, and location, made it more conspicuous than the runway environment and led the crew to misidentify it as the runway.

5. The reduced visibility and conspicuity of the runway environment diminished the crew’s ability to detect that they had misidentified the runway.

6. The lack of visual texture and other visual cues available over water contributed to the crew’s inability to detect the aircraft’s height above the water.

7. An increase in visual workload led to inadequate altitude monitoring, which reduced the crew’s situational awareness. As a result, the crew did not notice that the aircraft had descended below the normal 3° angle of descent to the runway threshold.

Findings as to risk

1. If the International Civil Aviation Organization Procedures for Air Navigation Services: Air Traffic Management are not implemented in the management of aerodrome light intensity, there is a risk that the optimal light intensity settings for prevailing weather conditions will not be selected.

2. If crews do not identify and manage threats, there is an increased risk of crew errors, which could lead to undesired aircraft states.

Other findings

1. Because the occurrence was originally assessed by WestJet as a non-reportable event, the cockpit voice recorder and the digital flight data recorder data were overwritten and were not available to the investigation.

The TSB reported the crew initiated the go around about 40 feet above water 0.3nm before the runway threshold. The first officer (ATPL, 12,500 hours total) was pilot flying, the captain (ATPL, 14,000 hours total) was pilot monitoring.

The aircraft was on final approach about 0.5nm before the missed approach point (MAP) fully established on a 3 degrees glideslope with a vertical rate of descent between 700 and 800 fpm, when the crew noticed a rain shower ahead and to their left, but had the shoreline in sight and anticipated to see the runway shortly, the crew decided to continue the approach visually. The pilot flying disconnected the autopilot, the aircraft pitched down from 0.5 degrees nose up to 1.2 degrees nose down, the autothrust system responded reducing the engine thrust from 62% to 52% N1, the rate of descent increased to 1150 fpm, the aircraft began to descend below the glide path. The aircraft crossed te MAP at 700 feet AGL. At the MAP the pilot flying indicated he had the runway in sight and began to roll the aircraft to the left until about 250 feet left of the extended runway center line.

The TSB continued to describe the events:

The flight crew saw neither the runway lights nor the PAPI lights during the approach, and did not request that the intensity of the lights be increased. After crossing MAPON, the aircraft entered the rain shower, which had moved toward the final approach path, reducing the visibility significantly. Eleven seconds later, when the aircraft was 1.5 nm from the runway on final approach and descending through 500 feet, the flight crew were advised that the wind was 060°M at 14 knots, gusting to 25 knots.

Approximately 1 nm from the runway, the aircraft exited the shower; the visibility sharply improved, and the crew realized that they had been tracking toward an incorrect visual reference, which was a hotel situated to the left of the runway. At this point, the aircraft was 190 feet AGL, descending at 940 fpm, rather than 320 feet AGL on a standard 3º angle of descent. Now able to see the actual runway, the crew recognized that the aircraft had deviated laterally to the left of the inbound final approach course, but they were not immediately able to assess their height above water. The PF advanced the throttles from 52% to 75% N1 and began to correct the lateral deviation, but the aircraft continued to descend at about 860 fpm.

At 1534:03, when the aircraft was 63 feet above the water, the aircraft’s enhanced ground proximity warning system (EGPWS) issued an aural alert of “TOO LOW, TERRAIN” and the PF increased the pitch to 4° nose up. The aircraft continued to descend, and a second aural alert of “TOO LOW, TERRAIN” sounded as it passed from 54 feet to 49 feet AGL (Figure 2).

At 1534:12, when the aircraft was 40 feet above the water and 0.3 nm from the runway threshold, the crew initiated a go-around. The lowest altitude recorded by the EGPWS during the descent had been 39 feet AGL.
After the go-around, the controller instructed the crew to conduct a holding pattern. Because the visibility was below the level required to conduct an approach (3600 m), the controller then closed Runway 10 for departures and instructed several other aircraft on approach to conduct holding patterns.

The TSB analysed:

The minimum visibility required to continue an approach to TNCM beyond the final approach fix is 3600 m. The air traffic controller cleared the flight crew for the RNAV Runway 10 approach when the aircraft was approximately 13 nm from the runway. Just after issuing the approach clearance, the controller advised the crew of the presence of moderate to heavy rain showers at the airport, but did not inform them of the updated visibility. Unaware that the visibility was below that required to conduct the approach, the crew continued the approach toward the runway.

Significant changes in visibility were not communicated to the crew, which allowed them to continue the approach when the visibility was below the minimum required to do so.

With respect to visual references the TSB analysed:

During the approach phase of flight, pilots may be prone to visual errors as they switch from scanning the instrument panel within the cockpit to scanning outside the aircraft to acquire visual references. The alternation of attention from one to the other increases their cognitive workload, the demand on their perceptual faculties, and the complexity of their flight-path monitoring tasks, particularly in conditions of reduced visibility. Conditions such as expectation bias and anticipation may also contribute to visual errors.

In this occurrence, the crew of an aircraft that had landed just ahead of WJA2652 had reported seeing the runway upon reaching minima. The crew of WJA2652 were expecting to see the runway shortly after crossing MAPON. The occurrence of a moderate to heavy rain shower, after the aircraft crossed MAPON, led to a significant reduction in visibility. The low-intensity setting of the runway lights and precision approach path indicator (PAPI) lights limited the visual references that were available to the crew to properly identify the runway.

Among the visual references that remained available, the features of a hotel located to the left of the runway, such as its colour, shape, and location, made it more conspicuous than the runway environment and led the crew to misidentify it as the runway. As the crew crossed MAPON, the PF advised that he had the runway in sight. He began to roll the aircraft to the left to align it with what he thought was the runway but what was actually the hotel.

The hotel located to the left of the runway appeared from a distance to be wider at its base and narrower on top than it actually was, causing it to appear similar to a runway. However, as the aircraft approached, it became more apparent that the shape was in fact a building. Those changing geometrics would have differed from what the pilot expected of an actual runway’s appearance on approach. Further, rain may have distorted visual references such as the hotel and made the changing geometric shape more difficult to interpret.

The reduced visibility and conspicuity of the runway environment diminished the crew’s ability to detect that they had misidentified the runway.

With respect to monitoring the flight path the TSB analysed:

In this occurrence, when the aircraft was on final approach prior to MAPON, a moderate to heavy rain shower ahead and to their left obscured the flight crew’s view of the airport environment and reduced their ability to identify the runway. After crossing MAPON, the crew encountered a greater reduction in forward visibility than they had anticipated when the aircraft entered the shower. The resulting increase in the crew’s visual workload led them to focus their attention on monitoring for external visual references and prevented them from adequately monitoring the aircraft’s altitude.

With respect to the delayed response to the EGPWS alert the TSB analysed:

At 63 feet above ground level (AGL), the flight crew unexpectedly received an EGPWS aural alert of “TOO LOW, TERRAIN,” which caused them to readjust their degraded situational awareness. On receipt of the aural alert, the crew carried out a “positive visual verification that no obstacle or terrain hazard exists” (as per both the aircraft manufacturer’s and operator’s recommendations for EGPWS alert response in daylight VMC), before deciding on a course of action. The PF increased the pitch to 4° nose up; however, as the aircraft continued descending, the crew received a second EGPWS alert when the aircraft was between 54 and 49 feet AGL.

While carrying out the positive visual verification, the crew’s ability to evaluate their height above the water was made more challenging by a lack of texture and other visual cues in the external environment, and it took them several seconds to understand that they were indeed too low. They initiated a go-around 9 seconds after the first EGPWS alert, by which time the aircraft had descended to 40 feet above the water. The alert response procedure recommended by the aircraft manufacturer and the operator led to a delayed response to the first EGPWS alert and resulted in the aircraft’s descent from 63 to 40 feet AGL before corrective action was taken.

Metars:
TNCM 072200Z 05017KT 9999 SCT018 BKN040 24/19 Q1019 A3009 NOSIG=
TNCM 072100Z 06010KT 9999 -SHRA FEW018 BKN035 23/22 Q1019 A3009 TEMPO SHRA=
TNCM 072000Z 05015KT 2000 -SHRA FEW016 OVC035 22/22 Q1019 A3009 TEMPO SHRA=
TNCM 071925Z 05021KT 2000 -SHRA FEW016 BKN035 22/21 Q1019 A3009=
TNCM 071900Z 05018KT 9999 FEW014 BKN035 24/21 Q1018 A3008 NOSIG=
TNCM 071800Z 05016KT 020V080 9999 FEW014TCU BKN035 25/21 Q1019 A3009 NOSIG=
TNCM 071700Z 05017KT 9999 VCSH SCT018TCU SCT035 25/21 Q1019 A3010 NOSIG RMK JP TO NE, N, S, W=
TNCM 071600Z 06016KT 9999 BKN018TCU 26/21 Q1019 A3011 NOSIG=
TNCM 071500Z 06014KT 030V090 9999 BKN016TCU 26/23 Q1020 A3012 RERA TEMPO SHRA RMK JP TO SE, S=
Aircraft Registration Data
Registration mark
C-GWSV
Country of Registration
Canada
Date of Registration
DmA qqhfnmjnmg Subscribe to unlock
Certification Basis
EfphhmnAng qAn cmhddndmfjhqfhcjbkdmkchmnkkgAqi Subscribe to unlock
TCDS Ident. No.
Dddj Subscribe to unlock
Manufacturer
Boeing
Aircraft Model / Type
737-8CT
ICAO Aircraft Type
B738
Year of Manufacture
KAqi Subscribe to unlock
Serial Number
KkmAm Subscribe to unlock
Aircraft Address / Mode S Code (HEX)
fpgcm Subscribe to unlock
Maximum Take off Mass (MTOM) [kg]
Hgpfd Subscribe to unlock
Engine Count
N Subscribe to unlock
Engine Type
Bl ch nej Subscribe to unlock
Main Owner
JclbggnkkdjlpfiAjjmgmmiddmAijfmkkhl mnlAg pbidp jkkpikiejgjc Subscribe to unlock

Aircraft registration data reproduced and distributed with the permission of the Government of Canada.

Incident Facts

Date of incident
Mar 7, 2017

Classification
Incident

Airline
Westjet Airlines

Flight number
WS-2652

Departure
Toronto, Canada

Destination
Sint Maarten, Sint Maarten

Aircraft Registration
C-GWSV

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

Airport
Princess Juliana International Airport, Saint Martin

Airport ICAO Code
TNCM

This article is published under license from Avherald.com. © of text by Avherald.com.
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