Amapola F50 at Helsinki on Nov 25th 2021, engine shut down in flight
Last Update: November 22, 2022 / 15:18:05 GMT/Zulu time
The aircraft remained on the ground in Helsinki for about 70 hours then positioned to Malmo (Sweden).
On Dec 1st 2021 Finland's Onnettomuustutkintakeskus (AIBF) reported the occurrence is being investigated by the AIBF. The Amapola F50 suffered an engine failure on takeoff.
On Nov 22nd 2022 the Onnettomuustutkintakeskus (AIBF) released their final report concluding the probable causes of the serious incident were:
1. The engine malfunction occurred during the final phase of the takeoff run when a signal discontinuity occurred in the autofeather unit connector and the unit activated. The left propeller feathered but the engine continued to operate. The pilots shut down the engine.
Conclusion: Upon signal interruption, the autofeather unit commanded feathering of the left propeller, but the engine continued to operate. Handling of similar situations is not drilled during pilot training.
2. An engine anomaly in a critical phase of the flight will increase the pilots' workload significantly, which may lead to the omission of procedural steps. Adherence to checklists will eliminate omissions during critical procedures.
Conclusion: The pilots failed to raise the landing gear due to high workload and because they did not conduct the after takeoff checklist.
3. Similar uncommanded feathering may occur unexpectedly in aircrafts fitted with the same engine type.
Conclusion: Pilots should be trained to recognize and handle uncommanded feathering.
4. The engine will not shut down during uncommanded feathering.
Conclusion: Engine power cannot be used effectively, while the feathered propeller overstresses the engine.
5. The captain's license did not contain a valid language proficiency endorsement.
Conclusion: Both the pilot and the airline should ensure that the pilot's license contains a valid language proficiency endorsement to enable the pilot to exercise the privileges of a flight crew member.
6. Helsinki-Vantaa airport has a dedicated ground frequencies. Air traffic control may instruct flight crews to contact the rescue service on these frequencies. These frequencies are not mentioned in flight crew documents.
Conclusion: A frequency that enables communication between rescue service and flight crews will help both parties to build situational awareness. The frequency should be readily available for flight crews.
7. Aircraft electrical connections and connectors cannot be inspected visually after connector installation.
Conclusion: Special attention must be paid on the condition and correct installation of connectors.
8. Air traffic controllers' alert pushbuttons are differentiated by color but not labeled for alert types. The colors are the same as the colors of the corresponding alert forms.
Conclusion: Before issuing an alert, controllers should use the color of the alert form to determine the pushbutton to be operated.
9. The sharing of responsibilities between the local controller and the approach controller could not be positively determined from the recordings.
Conclusion: Air traffic controllers shall agree positively on the responsibility for controlling a flight.
10. The abbreviation EM appeared in small red letters on the air traffic controllers' radar display without any other indications.
Conclusion: The appearance of the abbreviation EM in a radar label should be accompanied by an aural alert that would focus the controller's attention to the emergency situation.
The AIBF summarized the sequence of events:
After completing normal preflight preparations, the pilots began taxi towards runway 22L2 at 1501 h. Taxiing was uneventful, and at 1506 h takeoff was begun with the captain as the flying pilot (PF).
During the takeoff run, at a few knots below V1, the integrated alerting unit sounded two chimes, of which the second was of markedly shorter duration. The pilots also noticed that a warning flight on the central annunciator panel illuminated. Due to the momentary nature of these indications, neither pilot had sufficient time to diagnose the warnings.
The takeoff was continued past V1, and the PF rotated the aircraft at Vr. At the same moment, the master warning light illuminated and a triple chime aural alert sounded.
The PF should call landing gear retraction after liftoff; however, this call was not made, and the gear remained down throughout the entire flight. When airborne, the pilots normally conduct an after takeoff checklist, in which one item is gear retraction. Now the extended gear created significant drag and restricted the rate of climb to approximately 400 ft/min.
The PM reported a left engine malfunction after the aircraft had become airborne. The PF responded by instructing the PM to check and report the power settings on both engines. The engine instruments indicated that both were operating, but engine and propeller speeds on the left engine were abnormal. Engine speed was below the green arc, indicating that the propeller was providing 50 % of the total thrust. The PM confirmed these indications and added that the left propeller had not autofeathered. The PF then instructed to carry out the engine shutdown procedure. During the procedure, the PM shall ask the PF for an approval for shutting off fuel supply before moving the fuel lever to SHUT. This was given by the PF, who then told the PM to set a new heading in the flight management system.
Amapola Flyg's engine-out departure procedure for runway 22L calls for flying on heading 218 for 5 nm after takeoff before turning to waypoint VAVIS to enter a holding pattern at VAVIS.
As the aircraft was on climb to the single-engine acceleration height, the PM set code 7700 on the transponder and selected the traffic advisory (TA) mode on the traffic collision alerting system (TCAS).
The local controller (Tower, TWR) noted on his display that the flight was squawking 7700 and called the flight. The PM responded by transmitting mayday and reporting a left engine failure. The controller queried the pilots' intentions, adding that all runways at the airport were available for landing. The PM requested runway 15 and stated that the aircraft was on climb to the acceleration height and proceeding to VAVIS.
The controller discussed the situation with the approach controller and asked whether he should hand the flight over to approach control or keep it on the tower frequency, to which the approach controller replied that both options were acceptable. The flight remained on the tower frequency throughout the flight. The controller held an approach radar control rating for the airport and executed a combined local and approach controller's role during the remainder of the flight. He summoned additional controllers from a break into the control tower to assist in alerting actions and handling of telephone calls, while he himself concentrated on providing assistance and control service to the flight.
The aircraft increased speed after reaching the single-engine acceleration height, and at approximately 1,200 ft, about two minutes from takeoff, the PF told the PM to raise the flaps.
As lift reduced, the aircraft briefly lost approximately 100 ft of altitude, which triggered a ¡§don't sink¡¨ voice alert from the ground proximity warning system (GPWS).
The controller queried the aircraft's climb capability and was informed that the aircraft was able to climb and turn, but performance was degraded, rate of climb being no more than approximately 400 ft/min. The controller cleared the flight to climb to 3,000 ft MSL8. The flight had been initially cleared to 4,000 ft MSL in accordance with the standard departure procedure. Soon thereafter he noticed that the aircraft was heading towards a tall transmission tower (see para. 2.2.2) and instructed the flight to turn right, to the north. The turn momentarily took the flight outside the terminal control area into uncontrolled airspace.
The pilots discussed how to notify the cabin attendant of the situation and agreed that the PM informs the passengers of the engine malfunction and explains that the flight is returning to Helsinki in approximately ten minutes. They did not at first make a separate call to the cabin attendant, who received the information via the passenger address system. When the aircraft was on final approach, the PM briefed the cabin attendant on post-landing actions, explaining that the pilots' plan was to taxi to the apron and park the aircraft.
The pilots initiated the Quick Reference Handbook (QRH) engine failure procedure. Because the procedure does not call for raising the landing gear, the gear remained down throughout the remainder of the flight.
The controller advised that runway 04L was also available, but the pilots decided to use runway 15 and responded to this effect.
The pilots conducted the approach checklist including an approach briefing. While the PF was giving the briefing, the controller advised that visual approach was also possible, but the pilots stated that they would continue on present heading, complete the checklist and call back. They conducted a threat and error management (TEM) discussion on engine-out landing and post-landing actions.
Before the flight began approach, the controller asked, in Finnish, the pilots to report the number of persons on board (POB) and the amount of fuel, and inform the controller of any dangerous goods carried on board. By this point, the controller and the pilots had communicated in English, while intra-cockpit conversations had been in Swedish.
The PM stated that he would pass the required information in English in order to make the discussion understood by the PF. Several messages were exchanged until a mutual understanding was reached and the PM got POB reported. He did not report the amount of fuel and the presence of dangerous goods at first, and neither did the controller make further inquiries.
After the pilots had discussed altitudes, the PM requested that the flight could maintain 2,000 ft and reported ready for approach. The controller cleared the flight to 2,000 ft and advised that it was approximately 13 nm out for landing. He now queried the amount of fuel a second time, and the PM replied that the flight had 2,720 kg of fuel.
During the approach the PM called the cabin attendant advising that they would be landing shortly, and the cabin attendant replied that the cabin was ready.
The controller radar-vectored and cleared the flight for precision approach to runway 15.
Upon intercepting the localizer, the PF reported glideslope alive and told the PM to lower the flaps to the landing position. The aircraft intercepted and captured the glideslope.
The PF told the PM to lower the landing gear, to which the latter replied that the gear was down; the PF then asked whether the gear had remained down during the entire flight, and the PM replied in the affirmative.
The controller cleared the flight to land on runway 15, and landing took place at 1519 h. The aircraft vacated the runway at taxiway YF intersection and was marshalled to stand 124. The flight was completed at 1527 h.
Units of the airport rescue service that were standing by on the apron were stood down after the aircraft was parked.
The flight had remained on the tower frequency during the entire flight. Once the situation had normalized, the controller who had handled the flight asked that he would be relieved, and another controller took over the control position.
The AIBF analysed the takeoff run:
The transient nature of the alerts that occurred during the takeoff did not allow the pilots enough time to analyze the indications. The alerts activated when the nosewheels rolled over runway centerline lights. Noting that they did not recur, the pilots decided to continue the takeoff.
The same alerts had occurred, also momentarily, on the previous day during departure from Helsinki-Vantaa, but this had not been entered in the technical log. If a noted discrepancy is not shown in the technical log, the company's maintenance organization and other pilots that fly the affected aircraft will remain unaware of its existence. Transient discrepancies that cannot be traced to a specific system can be documented as a remark in the technical log so other pilots can anticipate the occurrence of possible system alerts and warnings. A remark will also notify the maintenance organization of a possible discrepancy, thus enabling early and correctly focused maintenance actions. If a discrepancy is left unreported or is not entered as a remark in the technical log, it may remain latent over an extended time.
The AIBF analysed the engine failure:
After the aircraft reached the decision speed (V1), the pilots continued the takeoff.
Approximately 2 s after passing V1, when the pilot had initiated rotation, an engine failure alert was received.
The Fokker 50 is powered by a variant of an engine family that is in extensive use in other aircraft types. The engine is not designed to shut down automatically if the propeller feathers.
Torque needed to rotate the propeller increases abruptly if the propeller feathers but the engine continues to operate, and if the engine is not shut down, the propeller or the engine may sustain damage.
In the Amapola Flyg incident, the pilots were confused momentarily when the propeller feathered uncommandedly while the engine continued to operate at a high power setting.
Warnings and alerts that indicate an engine failure or any other critical malfunction should be unambiguous to permit a correct and expeditious fault analysis.
The AIBF analysed the initial climb:
On the basis of the alerts received and of engine instrument indications, the monitoring pilot confirmed that an engine malfunction had occurred but the autofeather system had not activated. The left engine operated normally despite the fully feathered propeller.
The indicated propeller speed suggested a situation where an engine shuts down but the propeller does not feather. Although the alerts were indicative of an engine malfunction, the pilots failed to realize that the left engine continued to operate, and based on the alerts and engine instrument indications they elected to move the left fuel lever to SHUT to feather the left propeller. Shutting off fuel supply shuts down the engine and feathers the propeller.
The malfunction was caused by electrical discontinuity that occurred during the takeoff run in a connector in the left propeller feathering circuit and resulted from incorrect connector installation during engine maintenance. The discrepancy could not be detected visually because the connector pins were covered by the connector shell, and a shrink sleeve had been fitted over the connector. The discontinuity caused an erroneous signal that commanded propeller feathering. The engine remained in operation.
Engine power is increased automatically to meet power demands. While the activated feathering system will not adjust the affected engine's power setting, the drag of the feathered propeller increases power demand on the engine. In this incident, left engine torque exceeded the maximum permissible value due to an excessively coarse blade angle. Instrument indications remained correct throughout.
The pilots were trained for and practised emergency procedures for malfunctions that occur in an engine instead of the feathering system. One simulator exercise emulates a situation where an engine fails but the propeller does not autofeather.
Because the pilots had not encountered a similar problem either in flight or in the simulator, they experienced difficulties in conducting a timely and correct fault analysis. The fact that they were faced with an unfamiliar situation that they had not been trained for hampered the analysis and the handling of the anomaly. This distracted the pilots and contributed to the landing gear remaining down throughout the entire flight.
The pilots intended to continue the flight in accordance with the airline's engine-out procedure. The controller was not familiar with the engine-out procedures of various airlines, which led to momentary degradation of his situational awareness.
The controller noticed that the letters EM had appeared in red in the incident flight's radar label. This abbreviation will appear on the controller's display when a flight sets the emergency code 7700 on the transponder, but no audio alert will be received. The local controller called the approach controller upon becoming aware of the problem. Both controllers recognized the seriousness of the situation. The local controller asked the approach controller whether he should hand the flight over to approach control or keep it on the tower frequency, to which the latter replied that both options were acceptable. The flight remained on the tower frequency throughout the entire flight.
The controller became concerned when he noticed the aircraft's poor climb performance, and on top of that the aircraft was nearing a high obstacle. The controller queried the pilots' intentions, to which the pilot replied that the flight was on climb to the acceleration height and proceeding to waypoint VAVIS.
Because it seemed that the required vertical separation from the tall transmission tower in Kivenlahti could not be achieved in time, the controller instructed the flight to make a right turn to the north in order to maintain the required horizontal separation. Had the controller not intervened with the flight path, separation minima would most likely have been violated.
Even though heading and altitude instructions given by controllers should not take an aircraft into uncontrolled airspace, in this case the controller's intervention was necessary because of the close proximity of an obstacle, and it led to the aircraft exiting the control zone and entering uncontrolled airspace below the terminal control area for approximately 40 s during the turn due to degraded climb performance. Flight safety was not immediately jeopardized because aircraft operating below the terminal maneuvering area shall have their transponders on, which makes them visible on the controller's radar. Moreover, there was no other traffic in the vicinity.
Calculations for of engine-out procedures are based on a gear-up configuration and therefore do not take into account the possibility of the landing gear remaining extended. In this incident, the extended gear increased drag considerably and caused a marked degradation in the rate of climb. Although the pilots noted the degraded climb performance, they did not make attempts to analyse the anomaly or identify its causes.
In a high-workload situation, they initiated a Quick Reference Handbook checklist and failed to conduct the normal climb checklist, in which one item is gear-up selection. The engine-out Quick Reference Handbook checklist does not include a gear-up check.
This article is published under license from Avherald.com. © of text by Avherald.com.
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