Kiri

Saatja: Aivar Pau <[email protected]> Saadetud: 04.11.2019 11:34 Adressaat: Margit Palm <[email protected]> Teema: kommentaaripalve Tere, Loen lisaks tänasele leheloole allolevat OJK raportit ja siin on toodud ühe lennuõnnetuse põhjusena (p3) välja inststurktori otsus jätkata treeninglende korduvatele hoiatussignaalide vaatamata. Tunnen huvi teie kommentaari vastu: oli õppelennu jätkamine teie hinnangul korrektne, vaatamata korduvatele ELAC PITCH FAULT ECAM hoiatustele? Raport: https://www.ojk.ee/et/system/files/fail/manus/ee0180_es_san_investigation_report.pdf The investigation determined as the cause of this accident being a combination of the following factors: 1. the intermittent THSA override mechanism malfunction allowing to cause the loss of pitch control by both ELACs. This malfunction was due to the use of an inappropriate lubricating oil. The fact that the aircraft maintenance documentation does not require any test of the OVM during aircraft regular maintenance checks could have contributed to the result that the wrong oil in the OVM was left unnoticed during aircraft exploitation. 2. SEC design flaw allowing for a single event, the left landing gear temporary dedecompression, to cause the loss of pitch control by both SECs. The absence of ground spoilers arming for landing in the context of touch and go's training may have contributed to the temporary dedecompression of the left main landing gear. 3. The training instructor’s decision for continuation of the flight despite repetitive ELAC PITCH FAULT ECAM caution messages. The lack of clear framework of operational rules for training flights, especially concerning the application of the MEL, and the specific nature of operations that caused pressure to complete the training program may have impacted the crew’s decision-making process. The fact that ELAC 1 PITCH FAULT was left unreset lead to the degradation of the redundancy of the system. PIKEMALT During the flights as the crew received several ELAC PITCH FAULTs the TRI decided to follow the QRH, reset the failed computer and continue with the flights. Nevertheless, at 13:47 a F/CTL ELAC1 PITCH FAULT was triggered, that was not reset by the crew and what remained faulty until the end of the whole flight (including the accident). After finishing the training session with the third student at around 14:20 when the aircraft came to a full stop and before starting a training session with the forth student, the crew performed normal preparations for the flight. During that period MEL (figure 67) was not considered by the flight crew. This might be due to the fact that the crew was not aware of the fact that ELAC 1 was (still) faulty and because at the time of the event Airbus FCTM did not require to consider MEL on touch-and-go and stop-and-go training. In order to determine if this ECAM alert F/CTL ELAC1 PITCH FAULT that was left un reset was displayed (at 13:47 or later, due to inhibition), an analysis for the relevant FDR parameters was undertaken. The analysis showed that at 13:47:06, when the aircraft was touching the ground, the parameter “EL1PF” ESIB: A2802118 EECAIRS: EE0180 was switching to 1, referring to ELAC 1 PITCH FAULT being triggered, but not being displayed. At 13:47:42, when the aircraft was at 1668 ft RA, F/CTL page was called by the system. At 13:48:34, when the aircraft reached 2200 ft RA the F/CTL page was replaced by the STATUS page and at 13:48:38, the STATUS page was replaced by the CRUISE page. In case there are too many ECAM messages for the amount of space available in the lower part of the E/WD, a green arrow appears at the bottom of the display, pointing down to show that the information has overflowed off the screen. The pilot can scroll down to view additional messages by pushing the CLR pushbutton on the ECAM control panel (on the pedestal, just below the lower ECAM DU). It is important to note that when the messages are cleared, they do not reappear until the end of the flight. Cleared ECAM messages can be recalled when pushing the RCL pushbutton. In normal operations, this recall is requested by SOP before each flight during the Preliminary Cockpit Preparation and done by the flight crew by pressing the Recall (RCL) pushbutton during 3sec, displaying all alerts previously cleared via the CLR pushbutton that are still active and all alerts previously cancelled via the EMER CANC pushbutton. The sequence of SD pages is consistent with an ECAM alert F/CTL ELAC 1 PITCH FAULT displayed at 13:47:42, and cleared by the flight crew (by pressing the CLR p/b) at 13:48:34, and the same for the STATUS page at 13:48:38. According to the statements of all flight crew members, during the flight, each time as the ECAM display indicated the alert(s) F/CTL ELAC 1 and/or 2 PITCH FAULT, they acted accordingly to the QRH and reset the F/CTL computer(s). None of the crew members interviewed remember having ELAC 1 PITCH FAULT at 13:47 (during the flights with the third student), that was left in a faulty condition, nor they remember seeing1 the fault on the ECAM display when they started (nor during) the flight with the fourth student, however during approach they remember seeing CAT 3 SINGLE ONLY being presented on the ECAM status page. As the crew received several ELAC PITCH FAULTs, they remember having doubts about continuing the flight, but as the number of received faults was not limited in the FCOM or in the QRH, the TRI decided to continue with the flights. UURIMISES ELAC PITCH FAULT messages During the training flights the aircrafts` F/CTL system triggered several ELAC PITCH FAULTs while the instructor was manually stopping the trim wheel when the THS was returning to 0° after touch down (ground setting). The investigation revealed that the ELAC PITCH FAULT messages were originated from the intermittent failure of the THSA OVM. The ELAC PITCH FAULT was triggered by the computer in control (ELAC1 or ELAC2) due to erratic signals coming from the PTA micro- switches. The incorrect triggering of the PTA micro-switches was caused by a non-standard displacement of the OVM output piston which, in turn, was caused by a non-standard friction curve of the OVM clutch unit. The oil in the OVM was measured to be with almost twice of the viscosity of the oil required by the manufacturer. The higher viscosity of the oil most probably contributed to having a non-standard friction curve in the OVM clutch unit. The investigation could not confirm this hypothesis it by experiment data nor could determine a documented origin of the wrong oil in the THS. The fact that the aircraft maintenance documentation does not require any test of the OVM during aircraft regular maintenance checks could have contributed to the result that the wrong oil in the OVM was left unnoticed during aircraft exploitation. Additionally, as the ECAM caution messages were inhibited during approach, landing and take-off (see figure 22) and as they appeared after the aircraft passed 1500 ft, it made it hard for the flight crew to make a link between a hardware failure on landing and a repetitive computer failure messages appearing in level flight. This might have lead them to underestimate the problem as it was apparently solved by a single reset. The fact that the ELAC 1 was left un-reset by the crew following the last F/CTL ELAC1 PITCH FAULT cannot be fully explained by the investigation. Several ELAC PITCH FAULT warning messages were triggered as the TRI was manually stopping the trim wheel (at around 1° Nose Up) while the THS was returning to 0° after touch down. Due to an inhibition logic, these ECAM messages were displayed with a delay - when the aircraft was 1500 ft above ground level. JÄRELDUSTES • ELAC PITCH FAULT messages were originated from the intermittent failure of the THSA OVM. The ELAC PITCH FAULT was triggered by the computer in control (ELAC1 or ELAC2) due to erratic signals coming from the PTA micro-switches. The incorrect triggering of the PTA micro-switches was caused by a non-standard displacement of the OVM output piston which, in turn, was caused by a non-standard friction curve of the OVM clutch unit. The oil in the OVM was measured to be with almost twice of the viscosity of the oil required by the manufacturer. The higher viscosity of the oil might have contributed to having a non- standard friction curve in the OVM clutch unit. The investigation could not confirm this hypothesis it by experiment data nor could determine a documented origin of the wrong oil in the THS. • The crew made 5 resets to ELAC1 and 4 resets to ELAC2 according to QRH. • ELAC1 was not reset after ELAC 1 PITCH FAULT triggered at 13:47. • None of the crew members can recall the ELAC 1 PITCH FAULT being triggered nor displayed at 13:47 or any time later. Lugupidamisega Aivar Pau Postimees