Boeing 787-800 di Fiumicino, ANSV emana tre raccomandazioni di sicurezza

E', forse, una situazione “emergenziale”?

In solo 24 giorni, dopo che lo scorso 10 Agosto il velivolo B787-800 della Norwegian Long Haul, sul volo DY-7115 da Roma Fiumicino (Italy) a Los Angeles,CA (USA), dopo il decollo dalla pista 16R e l'avaria (esplosione?) di un propulsore RR Trent 1000, con pezzi di metallo dello stesso motore caduti su caseggiati e auto sottostanti e rientro dal volo, è stata varata una iniziativa, quasi, immediata.

ANSV in relazione all’inconveniente grave in questione ha pertanto emanato, a fronte di una inchiesta ancora in corso, tre raccomandazioni di sicurezza, indirizzate all’EASA (European Union Aviation Safety Agency) e, in sostanza alle aerolinee che operano con questa tipologia di propulsori. La stessa EASA quale organismo di certificazione del propulsore in questione sarebbe, peraltro, direttamente interessata alle criticità emerse sul Trent 1000.

On Sep 4th 2019 the ANSV released three safety recommendations explaining the motivation for those recommendations were:

the borescope inspection of the engine Trent 1000 G/01A SN 10166, performed after the IFSD event occurred to the B787-8 registration marks LN-LND, highlighted the fracture of two IPT blades. One of these is attributable to the same corrosion fatigue fracture mechanism that was responsible for ten previous cases of IFSD in the Trent 1000 fleet. In one of those cases, in addition to IFSD the blade release also caused damage on the LPT drive arm, proving further negative effects on safety could be possible as a consequence of a IPT blade fracture beside what happened in the B787-8 marks LN-LND event, in which damages to the aircraft and to objects on the ground were recorded. Indeed, for this matter EASA has already recognized the need to maintain fleet safety and has mandated several Rolls-Royce recommended safety actions in the last two years through 6 ADs, the latest and only live action being issued in NMSB 72-AK186, which instructs a hard life for pre-modification blades and is mandated by EASA AD 2019-0135. However, the in-flight IPT blade failure of the Trent 1000 G/01A SN 10166 happened 200 flight cycles before the hard life limit, demonstrating this not sufficient to avoid detrimental effects on safety.

The ANSV recommends to EASA:

Safety Recommendation ANSV-9/1147-19/1/I/19.

To take immediate actions to achieve an higher level of safety, also taking in consideration, but not limiting EASA initiatives to, defining different and more stringent time limits for the Trent 1000 pre-mod 72-H818 IPT blades.

Safety Recommendation ANSV-10/1147-19/2/I/19.

To re-evaluate the whole validity of the service management adopted by the manufacturer for the Trent 1000 pre-mod 72-H818 IPT blades, endorsed by the AD 2019-0135.

Safety Recommendation ANSV-11/1147-19/3/I/19.

To evaluate provisions relevant to the de-pairing of pre-mod 72-H818 engines, avoiding two engines of the same pre-mod status being installed on the same aircraft, thus further lessening the possibility of a DIFSD.

The ANSV reports that at about 1200 feet and 200 knots over ground climbing out of runway 16R the left hand engine vibration warning activated followed by “EEC MODE L”, “LOSS OF TPR L”, “ENG L EGT RED” (UTC 14.46.14), “ENG LIMIT EXCEED L” (UTC 14.46.16) and “OVERHEAT ENG L” (UTC 14.46.20) EICAS fault messages. The crew shut the engine down and returned to Fiumicino Airport. About 4kg of debris was recovered. 

The ANSV released following preliminary data analysis:

Following the event, data were downloaded on site from the Engine Monitoring Unit (EMU) and from the Continuous Parameter Log (CPL). The Enhanced Airborne Flight Recorders (EAFR, picture 11) were downloaded at the ANSV laboratories.

The preliminary analysis of the EAFR data shows that at 14.46.05 UTC (about 6 s before the “Eng1_Vib_Warn” discrete parameter activation) an abrupt decrease of left engine N1 (from 90% to less than 60%, figure 4). At the same time, left engine N2 and N3, oil temperature and pressure slightly increased (figure 5). From the point onward the overall vibration level of the left engine increased (figure 6/7). The left engine IFSD was commanded by the crew at 14.48.06 UTC. The engine manufacturer reviewed the EMU (5 Hz sampling rate) data, confirming the above evidence as well as highlighting, in addition, that the behavior of the engine was compatible with an Intermediate Pressure Turbine (IPT) blade damage. In more detail, the EMU data shows that the drop in N1 happened after IP tracked order vibration increased (as a result of the IPT blade release). Therefore, the most likely sequence of events is (figure 8):

- IPT blade release resulting in IP tracked order vibration increase;

- IPT blade release causes downstream damage to the LP turbine and a reduction in LP shaft speed and increase in LP tracked order vibration;

- the engine control system then attempts to restore power before the pilot shuts down the engine.

No significant variations in the vibration level or other engine related parameters were recorded from the left engine prior to the event.