A Smartwings Boeing 737-800, registration OK-TVO performing flight QS-1125 from Samos (Greece) to Prague (Czech Republic) with 170 people on board, was enroute at FL360 over the Aegean Sea about 100nm northeast of Athens (Greece) when the crew drifted the aircraft down to FL240 and continued to Prague at FL240 for a landing without further incident about 2:20 hours later.
The Aviation Herald received information that the #1 engine (CFM56, left hand) shut down spontaneously while enroute at FL360. The crew descended the aircraft to FL240, worked the related checklists and attempted to relight the engine twice, first using windmilling and then using crossbleed, the engine however did not restart. As there was sufficient fuel on board the crew decided to continue to Prague nonetheless.
The occurrence aircraft returned to service about 17 hours after landing in Prague.
On Aug 24th 2019 The Aviation Herald received additional information stating maintenance performed a wet run of the engine after landing, which failed, the engine valve closed light remained illuminated and no fuel was supplied to the engine. Maintenance subsequently replaced the hydro mechanical unit (HMU), fuel filter nozzle, servo fuel heater, fuel pump and fuel heat exchanger, subsequently a test 5 - power assurance test - was performed and was passed.
On Aug 24th 2019 the airline confirmed the occurrence to Czech Media, e.g. irozhlas and zdopravy stating: "The crew proceeded in accordance with the safety and operational procedures for these cases and the aircraft landed safely. The commander is one of the most experienced in the company, the crew was in control of the situation and certainly would not underestimate anything."
On Aug 23rd 2019 (verified by AVH on Aug 25th 2019) Reader Marc had reported in the reader comments:
I work at Budapest ACC and I was in contact with this A/C when they overflew Hungary. Not a word did they mention about engine failure we were informed about a "technical issue". That is in most cases an air con failure for the 737 to fly at 240 or 250. So they came in at FL240 as they reached the Austrian border we sent them to Vienna Approach.
10 minutes later they called us back to inquire us why we haven't told them about the engine failure. It turned out that the failure was announced over Prague, Vienna then called us back but we didn't know either. Serbians were also unaware and I also asked my colleague who was working at KFOR (Kosovo) airspace - it is also operated from Budapest - but he didn't know either.
I think that tells a lot about this airline. And just to add: This evening I had 2 A/C in 20 minutes from this operator on my frequency cruising at 250 so it's not so unusual to see the like that.
On Aug 26th 2019 Czechia's Civil Aviation Authority told Czech media that the aircraft did not land at the nearest suitable airport although required by standard operating procedures and regulations. Between Samos and Prague there were several suitable airports nearer than Prague. The CAA pledged: "Therefore, in cooperation with its partners, the Civil Aviation Authority, across specialized services, collects available information, evaluates it and takes action after evaluation. Whether this will result in an administrative proceeding with the commander, the company, or even the filing of a criminal complaint cannot be predicted at the moment, CAA will make every effort to prevent a similar scenario from happening again. In particular, our goal is to rectify the system."
Czechia's UZPLN (Accident Investigation Unit) is also going to investigate the occurrence.
On Aug 26th 2019 The Aviation Herald received information, that the CVR was already overwritten by the subsequent flights, the FDR data of the occurrence flight however could be downloaded successfully. This investigation started only after The Aviation Herald published the occurrence on Aug 23rd 2019.
On Sep 13th 2019 The Aviation Herald learned that an internal investigation conducted by Smartwings identified there was no systemic fault, but a crew error. The captain of the flight, at that time head of flight operations of Smartwings, is no longer head of flight operations, his deputy has now taken that position. The captain continues to fly for the airline and maintains privileges as instructor, examiner and TRE. Czechia's CAA is determined to ensure that such a decision is not taken again in the future and pledges very harsh penalties. Surrounding nations also show significant interest in the ongoing investigation, revocations of overflight permits are being discussed.
On Oct 11th 2019 Czechia's CAA wrote to The Aviation Herald: "First of all I would like to apologize for the delay of my response. And I would like to inform you that this information was not known to us before your email." On Sep 14th 2019 The Aviation Herald had received new information and therefore had sent e-mails to Czechia's CAA and UZPLN writing: "While OK-TVO was still airborne south of Hungarian Airspace (after the engine shut down over the Aegean Sea), the office of Smartwings is said to have contacted a Budapest based maintenance provider about whether they would have spare parts readily available, the fuel supply of one of the engines was blocked. Subsequently it was decided the aircraft would not land in Budapest."
On Oct 24th 2019 Czechia's UZPLN reported in their 3rd quarter 2019 bulletin, that the aircraft was enroute at FL360 when the #1 engine failed. The crew reported a "maintenance issue" to ATC and requested to descend to FL240. No PAN or emergency call was issued. The crew attempted to restart the engine twice unsuccessfully. The captain tagged the nearest suitable aerodrome to be Prague and continued to Prague without informing any of the ATC stations along the 2:20 hours route about the engine failure until in contact with Prague Air Traffic Control, when the crew declared PAN and reported the failure of the #1 engine. The aircraft landed. A fuel pump caused the engine to starve, metallic chips were found in the fuel filter. Both parts were shipped for expert examination. An investigation into the occurrence rated a serious incident is continuing.
On Nov 27th 2019 it became known, that Czechia's District Prosecution Office have opened criminal proceedings and police investigation into the occurrence for suspicion of committing a crime of endangering the public due to negligence.
On Jul 23rd 2020 Czechia's UZPLN released their final report in Czech only (Editorial note: to serve the purpose of global prevention of the repeat of causes leading to an occurrence an additional timely release of all occurrence reports in the only world spanning aviation language English would be necessary, a Czech only release does not achieve this purpose as set by ICAO annex 13 and just forces many aviators to waste much more time and effort each in trying to understand the circumstances leading to the occurrence. Aviators operating internationally are required to read/speak English besides their local language, investigators need to be able to read/write/speak English to communicate with their counterparts all around the globe). The report concludes the probable causes of the serious incident were:
The probable cause of the serious incident was following the loss of a propulsion unit a faulty decision making process by the aircraft commander that did not comply with the Quick Reference Handbook (QRH) and Flight Crew Training Manual (FCTM). These procedures are binding.
The sequence of events:
- according to the Defect Logbook entry 107847 the fuel pump was running dry before the incident flight
- operation of the fuel pump running dry during the incident flight without fuel as lubricant
- shutdown of the engine and subsequent loss of the propulsion unit
- obvious disregard and violation of applicable Operation Manual Air Traffic Procedures as well as applicable regulations, provisions and safety recommendations
- defective determination of a suitable aerodrome for safe landing with a failed engine following fuel pump failure
- poor implementation of fuel policy
- the pilot in command did not follow the principles of Cockpit Resource Management while performing the QRH's non-normal checklist (NNC) procedures and thus made it impossible for the first officer to participate effectively in the decision making process
- failure to complete the relevant NNC QRH procedure point 10 "plan to land at the nearest suitable airport", the commander avoided the obligation to make a safe landing at the nearest suitable aerodrome as specified by the aircraft manufacturer's QRH and FCTM valid in commercial air transport
- it can not be satisfactorily demonstrated, but neither reliably ruled out, that the decisions made by the aircraft commander and at the same time the flight director of the operator were influenced by economic aspects.
The UZPLN summarized the interview of the captain stating that the captain did not notice any difference in engine performance during preparation for departure, takeoff and climb, if there was any difference it was indistinctive. When enroute at FL360 the engine ran down, the captain did not consider whether it was a flame out but began to work to solve the issue, determined the appropriate level of the aircraft for the weight of the aircraft and then used "used a wrong phrase maintenance issue" when requesting the descent to FL240. There was a misunderstanding with ATC regarding the flight level and after receiving clearance to descend to the requested flight level the captain did not believe that ATC would have been more helpful after a PAN PAN declaration or notification of an engine out and added that he was reluctant to report on a specific issue on frequency. It was necessary to use maximum continous thrust to maintain level and speed. Taking into account "Airport, Equipment, Weather" the captain opted for Prague considering that according to the operational flight plan they had sufficient fuel on board (due to tankering). While attempting to restart the engines they transferred to Athens Area Control Center, where the captain used the wording that they continued to Prague to make clear they were still following their planned route until they had made a determination where to divert to. There was a mutual agreement between the pilots that Budapest was the alternate for Prague. Thessaloniki was ruled out, Belgrade was right below them, he ruled Vienna out due to traffic. The captain was aware that the aircraft was not ETOPS certified, however, Boeing also did not set a range limitation. The captain did not recall how much fuel was left on board after landing. The first officer's actions were helpful to the captain.
The captain (53, ATPL, 20,900 hours total, 8,069 hours on type) was pilot monitoring, the first officer (35, ATPL, 3,400 hours total, 2,488 hours on type) was pilot flying.
Weather information around did not show any adverse weather for any of the possible aerodromes around like Samos, Kavalas, Thessaloniki, Athens, Sofia or Belgrade. The investigation determined a choice of three airports, that could be selected as nearest suitable aerodrome following the engine shut down and attempted two restarts: Kavalas (LGKV), Sofia (LBSF) or Belgrade (LYBE).
More than 100 chips and fragments of 1 to 10mm in size were found at the main fuel filter, the particles mainly consisted of aluminium-copper-magnesium as well as aluminium and silicone. The main fuel filter was not the cause of the fuel pump failure.
The fuel nozzle filter was found contaminated with more than 100 pieces of copper alloy (copper, tin lead), the nozzle filter was not found to be the cause of the fuel pump failure.
The Hydromechanical Unit (HMU) was completely disassembled and was found with a high number of bronze-coloured splinters and fragments, that affected the activity of several moving parts of the HMU, in particular the pressure/shut-off valve which was found in the closed position and heavily contaminated with bronze coloured splinters and fragments causing the valve plunger to become sticky and hardly movable.
The main fuel pump was contaminated with more than 100 chips and fragments sized 1-10mm of aluminium-copper-magnesium and aluminium-silicone. Additional contaminants contained copper, nickel, lead alloy, carbon, fluorine and aluminimum. The rotary part of the fuel pump showed wear by dry friction. The pump housing showed friction marks with the impeller (rotating part of the fuel pump). On the pump closet traces of melted metal were found proving high operating temperatures likely caused by dry running the fuel pump, i.e. without fuel as lubricant.
The UZPLN analysed that the captain did not use PAN PAN to make urgency clear to ATC, ATC thus continued to process the aircraft based on priority. The first officer, pilot flying, knew that they needed to descend within 2 minutes following the engine failure, increasing nervosity on the flight deck, declining airspeed did not prompt the captain to change his mind. When the speed had dropped to 226 KIAS the first officer prepared for an offset procedure in case they needed to descend without ATC clearance when the airspeed would drop below safe maneouvering speed. These risks prompted the first officer to become more and more assertive towards the captain to get the descent cleared. The Operations Manual clearly defines the obligation to report the circumstances in a relevant and correct manner to enable ATC to properly deal with the situation (loss of ability to maintain flight level). While the first officer as pilot flying was responsible to safely fly the aircraft the commander failed his tasks by ignoring the communication causing developing stress on the flight deck for more than 2 minutes. The captain reported maintenance issues three or four times and only reported the engine failure with Prague Area Control Center.
The captain could not know whether the engine shut down due to contaminated fuel and failed to adopt a safety strategy in case of the other engine failing, too.
The delayed clearance to descent could have caused the first officer to need to initiate an emergency maneouver to adopt an offset path and descent without clearance and proper separation with other air traffic. The maneouver would likely have been abrupt so that unrestrained passengers might receive injuries. The time lost in communication, which was not assessed as a potential risk by the captain, prevented the first officer from being ahead of the aircraft and being ahead in dealing with the circumstances.
After the engine failed the crew attempted two air restarts, first by windmilling and the second by cross bleed, according to the NNC, however, without success. Point 10 of the NNC then states: "Plan to land at nearest suitable airport", the NNC also mentions to not rely on FMC performance computations and predictions.
The captain did not perform the procedure to secure the CVR.
The CRM showed an enormeous command gradient in the cockpit, which led to the fact that the first officer did not participate in the decision making processes. Average rating of the commander's CRM was "very poor".
The drift down altitude for the aircraft's weight was determined by the investigation as 24090 feet, however, the usable pressure altitude was 22,788 feet. Hence the nearest flight level was not FL240, but FL220 for drift down.
According to the operational flight plan the aircraft departed with 9,460 kg of fuel due to fuel tankering (the aircraft had departed Prague with 15,500kg of fuel on board to avoid refueling in Samos). The required fuel amount for the flight from Samos to Prague was 9,217 kg (including final fuel reserve, diversion fuel, ...). After landing in Prague 2,340kg of fuel were remaining on board (1083 kg final fuel reserve). However, the aircraft would have needed 2412kg of fuel on board had they needed to divert from Prague to their alternate according to their operational flight plan, which does not take into account the single engine operation and increased fuel consumption. The captain thus would have been required to declare Mayday before reaching their alternate.
The investigation also analysed that the slight difference of 1.5% in engine performance between left and right hand engine could have changed the departure runway computations and lost the safety margin of 122 meters on the 2100 meters long runway. As result, in case of a slight hesitation to reject takeoff at V1, the aircraft could have overrun the end of the runway or in case of a continued takeoff become airborne only past the end of the runway.
The commander had accumulated 20,900 hours total flight time, was flight instructor and flight examiner and was flight director of his operator for more than 15 years. As such he had great aviation knowledge and experience. He had approved binding documents like OM, QRH, FCTM, FCOM for his operator. It is thus difficult to understand that during one flight he ignored, violated and denied the obligations resulting from the binding OM, QRH, FCTM and FCOM as well as regulations and safety recommendations. The decision making process by the commander did not proceed according to the defined QRH NNC procedures.
It was not possible to satisfactorily assess the influence of the corporate attitude and management culture onto the decision making process. It was also not possible to determine satisfactorily whether and how economic aspects affected the commander's decisions.
Although the commander stated in his resignation message that he did not decide based on economic considerations there was a discrepancy between the actual execution of the flight and the termination message.