Hokkaido SF34 at Okushiri on Jun 4th 2011, engines overtorqued on go-around

Last Update: November 28, 2014 / 18:40:16 GMT/Zulu time

Bookmark this article
Incident Facts

Date of incident
Jun 4, 2011

Classification
Incident

Aircraft Type
SAAB 340

ICAO Type Designator
SF34

On Nov 28th 2014 the JTSB released their final report concluding the probable causes of the serious incident were:

In this serious incident, during the approach to Runway 31 of Okushiri Airport, the Aircraft executed a go-around and once started climbing but it soon reverted to descend and came close to the ground. Consequently, flight crewmembers came to realize the situation and executed an emergency operation to avoid crash to the ground.

It is highly probable that the Aircraft’s descent and approach to the ground was caused by the following factors:

(1) The PIC followed the Flight Director command bar instructions, which indicated the descent because the altitude setting was not changed to the initial go around altitude, and subsequently the PIC made the Aircraft descend even lower than the FD command bar instructions.
(2) The PIC and the FO could not notice descending of the Aircraft and their recovery maneuvers got delayed.

It is highly probable that these findings resulted from the fact that the PIC could not perform a fundamental instrument flight, the PIC and the FO used the Autopilot/Flight Director System in an inappropriate manner without confirming the flight instruments and the flight modes, and the FO could not transiently carry out closer monitor of the flight instruments because of the other operations to be done.

Moreover, it is probable that the FO’s operation of engaging an autopilot and changing the vertical mode to make the Aircraft climb by using the Autopilot/Flight Director System eventually became a factor to delay recovery maneuvers against ground proximity.

It is probable that the Company didn’t create a standard procedure, reflecting the contents of Aircraft Operating Manual, for its crewmembers to confirm and call out the changes mode, without noticing its importance and didn’t carry out adequate training. Furthermore, it is probable that the PIC and the FO excessively relied on the autoflight system.

The JTSB reported that the captain (41, ATPL, 5,144 hours total, 4,602 hours on type) was pilot flying, the first officer (30, CPL, 2,980 hours total, 2,661 hours on type) was pilot monitoring.

The crew performed a VOR approach, MDA 600 feet MSL, using the autopilot with the target altitude set to the MDA of 600 feet and vertical speed mode to descend towards the MDA. The autopilot descended to the target altitude and levelled off at 600 feet changing into autopilot vertical mode ALTS, the target altitude had not been reset to the go-around altitude of 4000 feet in the altitude window.

After passing the missed approach point the crew pressed TOGA, the autopilot went into go-around and the engines began to accelerate to TOGA power, the vertical mode however immediately reverted back to ALTS seeing the aircraft at the target altitude.

The autopilot was disconnected and the aircraft began to climb and while gear and flaps were retracted. Climbing through 750 feet the aircraft began to descend again, the autopilot was engaged shortly afterwards (as the aircraft descended through 650 feet), the active modes were HDG lateral and ALTS vertically (capture of target altitude 600 feet, vertical speed mode), 2 seconds later the indication ALTS disappeared and the autopilot descended the aircraft to below 600 feet MSL. Descending through about 500 feet MSL (270 feet AGL) the terrain awareness and warning system (TAWS) issued a "Sink Rate" call, 3 seconds later the power levers were firewalled at the maximum power setting above engine limits, another second later the TAWS issued a "TOO LOW, TERRAIN!" warning, at that point the radio altitude had reduced to 92 feet AGL (the TAWS actually recorded 87.8 feet AGL), the aircraft's speed was 213 KIAS. The autopilot was disconnected and the aircraft pitched up sharply from a nose down pitch angle to 9.5 degrees nose up within one second resulting in the vertical acceleration peaking momentarily at +4.1G.

The aircraft subsequently climbed to 4000 feet and entered a hold before returning to Hakodate for a safe landing.

The JTSB analysed that the weather, despite fog and low visibility prompting the go-around after the crew did not establish visual contact at the missed approach point, did not contribute to the serious incident.

The JTSB analysed that the go-around altitude must be selected into the altitude window prior to engaging the TOGA button and wrote: "It is probable that both pilots were focused on identifying the runway because the prevailing weather condition wasn’t good as described in 3.3. It is highly probable that they didn’t change the altitude setting to APA, which remain unchanged of 600ft."

The JTSB analysed that immediately following the decision to go around it was highly probable that the first officer, upon instruction by the pilot flying, was busy with setting engine power to 100%, retracting gear and flaps, monitoring engine instruments, vertical speed indicator and other instruments to verify the aircraft was in the initial climb.

Although the autopilot was disengaged, the autoflight system continued adjusting the flight director bars. The autoflight system had switched to GO-Around setting the lateral channel to ROLL GA, the vertical channel however immediately returned to ALTS (maintain selected altitude) with the target altitude still selected at 600 feet and the aircraft close to that altitude. The flight director bars therefore required a descent while the aircraft initially climbed.

About 4 seconds after the go-around was initiated, the nose of the aircraft began to lower again, the aircraft peaked at 750 feet MSL and began to descend again, probably because the pilot flying reverted to follow the flight director bars.

The JTSB wrote: "It is highly probable that because the PIC did not confirm the basic flight instruments such as the altimeter, the airspeed indicator and the vertical speed indicator in an appropriate manner, he could not realize that the Aircraft didn’t established its climb and he made the Aircraft descend without his intention. It is highly probable that the PIC could not perform a fundamental instrument flight at this time. The objectives of operations during go-around is “climbing turn to the safety side.” Therefore, the PIC should have realized that the objectives would not be achieved if he followed the FD command bar directions. It is somewhat likely that the PIC paid excessive attention to his own “FD Follow” principle and he became unaware of the objective of the operations."

With respect to the first officer the JTSB wrote: "Considering these conditions, it is probable that the FO could not monitor the instruments temporarily and failed to pay close attention to the instruments, and he could not realize that the nose of the Aircraft was going lower since the nose of the Aircraft went down gradually during that time. The FO didn’t realize that the Aircraft was descending, though it was necessary to establish its climbing attitude. It is probable that it was difficult for the FO to feel descending since the Aircraft was accelerating as described in 3.4.3 (2) and the FO assumed that the Aircraft would climb as usual since he had already checked the initial climb immediately after executing the go-around operation."

While the aircraft accelerated and the flaps were retracted from 7 to 0 degrees, the autopilot was re-engaged, the aircraft was descending through 650 feet at that point already and the autopilot therefore used the current rate of descent as target for the vertical speed. the JTSB annotated however that the first officer, pilot monitoring, did not remember to have engaged the autopilot, standard operating procedures required the pilot monitoring to engage the autopilot on pilot flying's order.

The JTSB analysed that the captain believed he was still flying manually and was not aware of the autopilot being engaged. Hence it was likely the first officer engaged the autopilot.

The JTSB analysed that simulator tests showed, that when the autopilot is engaged in the midst of the capture zone for the target altitude, the autopilot engages in vertical speed mode briefly then reverts to ALTS (target altitude capture). However, it was probable that soon after the autopilot engaged in ALTS re-capturing 600 feet MSL the altitude window was selected to 4000 feet cancelling the ALTS mode, which returned to vertical speed mode causing the aircraft to descend below target altitude.

The JTSB wrote: "In any case, it is probable that the FO tried to make the Aircraft climb by using the AP/FD system. The Aircraft continued descending with autopilot engaged and ALTS changed to VS in the vertical mode during descent. It is highly probable that the Aircraft descended continuously because the Aircraft could not respond to repeated mode changes in short period."

Following the "SINK RATE" call it was highly probable, that the commander realized the aircraft was in a dangerous situation, pushed the thrust levers to their maximum power position and pulled the yoke needing more power than usual as he was working against the autopilot. The first officer joined in pulling the elevator, the aircraft pitched up abruptedly resulting in a +4.1G vertical acceleration, the aircraft settled in a climb. The JTSB concluded that section of analysis: "As described in 3.4.4 (1) and (3), it is probable that the FO’s operation, engaging autopilot and changing the vertical mode to make the Aircraft climb with the AP/FD system, eventually contributed to delaying the operation to avoid ground proximity."

The JTSB analysed with respect to cockpit resource management: "It is highly probable that the PIC and the FO had failed to exercise basic situational awareness, since they descent the Aircraft despite a phase of go-around and they did not notice the feet that the Aircraft was descending without proper check of flight instruments and modes of flight, in this serious incident. It is highly probable that the team of the PIC and the FO didn’t share their intentions and tasks well because they didn’t have good communication and coordination in an appropriate manner, such as changing mode and engaging autopilot by FO without the PIC’s approval."

The JTSB stated that after the crew had informed their company about the occurrence, the company did not initiate an inspection of the aircraft and did not set priority to secure the flight data recordings. The JTSB wrote: "As described in 2.4.4 and 2.12, the Aircraft was in a situation which requires inspections of aircraft and engine in view of its excessive vertical acceleration and engine torque values. But the Company did not perform these inspections and let it fly as it is. There are some differences in the event’s report between the PIC and the FO, even so, it is probable that the Company would have been able to examine the specific contents of the flight in the early stages if Manager A had put top priority on securing safe flight and shared information within the Company."
Incident Facts

Date of incident
Jun 4, 2011

Classification
Incident

Aircraft Type
SAAB 340

ICAO Type Designator
SF34

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

You can read 2 more free articles without a subscription.

Subscribe now and continue reading without any limits!

Are you a subscriber? Login
Subscribe

Read unlimited articles and receive our daily update briefing. Gain better insights into what is happening in commercial aviation safety.

Send tip

Support AeroInside by sending a small tip amount.

Related articles

Newest articles

Subscribe today

Are you researching aviation incidents? Get access to AeroInside Insights, unlimited read access and receive the daily newsletter.

Pick your plan and subscribe

Partner

Blockaviation logo

A new way to document and demonstrate airworthiness compliance and aircraft value. Find out more.

ELITE Logo

ELITE Simulation Solutions is a leading global provider of Flight Simulation Training Devices, IFR training software as well as flight controls and related services. Find out more.

Blue Altitude Logo

Your regulation partner, specialists in aviation safety and compliance; providing training, auditing, and consultancy services. Find out more.

AeroInside Blog
Popular aircraft
Airbus A320
Boeing 737-800
Boeing 737-800 MAX
Popular airlines
American Airlines
United
Delta
Air Canada
Lufthansa
British Airways