Missing AirAsia flight QZ8501, a detailed view of the event

The A320 – 216 (MSN 3648) used on Flight QZ8501 was delivered in on October 16, 2008, from Airbus’ manufacturing hub in Toulouse, France with CFM engines, has flown 13,600 times, covering 23,000 hours, and underwent its last maintenance on Nov 16, 2014. The captain Iriyanto had more than 20,500 flight hours, almost 7,000 of them with AirAsia. It’s monsoon season in the region and there were heavy thunderstorms in the area. Dense storm clouds were reported in the area at the time the plane lost contact. The tops of thunder storms can reach over 30,000 feet and pilots try to avoid them. As per Flight radar 24 and most planes in that area are diverting around due to severe weather. The pilot contacted Jakarta air traffic control 6:12 a.m. reporting clouds and asking for permission to turn left and to go higher from 9,700 meters (32,000 feet) to climb to 38,000 ft (11,000m) to avoid the clouds but the request could not be approved at that time due to traffic, there was a flight above, and five minutes later flight QZ8501 disappeared from radar. The plane’s last reported altitude was 32,000 feet near Belitung Island in the Java Sea and as per the radar plots the plane was flying at 353 knots, 100 knots slower than it should have been. There was no distress signal from Flight QZ8501. The contact was lost about 42 minutes after the single-aisle jetliner took off from Indonesia’s Surabaya airport – about an hour before it was scheduled to land in Singapore. Far too many airline crashes can be directly linked to the pilot having incomplete information about the condition of the aircraft.

QZ8501 missing AirAsia flight
The missing aircraft, PK-AXC, was delivered in September, 2008. It was operated by subsidiary Indonesia AirAsia, which operates a fleet of 30 A320s. Across all of its subsidiaries, AirAsia operates 170 A320s.

Updrafts and downdrafts of 5,000 ft/min can take control of large aircrafts. Weather satellite images showed extremely turbulent conditions (5am local time). One of the challenges of flying across the Equator is the storms in the Inter Tropic Convergence Zone (ITCZ) can go up to 50,000 ft and extend up to 600 miles. Could it be possible that before the pilot he could effectively climb above the severe weather cell still developing,run into a series of lighting strikes, temporarily disabling or re-seting the Fly-by-wire system to a null condition status. In the mean time the aircraft is without full and effective control, putting the aircraft in a situation where it could cause stall or vertically accelerate out of control and structurally breaking apaŕt.

AirAsia group of companies in South East Asia, it should be noted that this flight belongs to Indonesia AirAsia,. They use the IATA Code – QZ. Indonesia AirAsia has a majority of Indonesian shareholders. Other airlines in the AirAsia family – AirAsia Berhad (IATA – AK); AirAsia X (IATA – D7); Thai AirAsia (IATA – FD); AirAsia Zest (IATA – Z2); Philippines AirAsia (IATA – PQ) & AirAsia India (IATA – I5) are related to Indonesia AirAsia but are not directly affected.

Singapore Airlines flies Boeing 777s, A380s, and A330s-all powered by Rolls Royce Engines. Singapore Airlines’ subsidiary-Silk Air-flies A320 and A319 aircraft fitted with IAE engines. Tigerair, in which Singapore Airlines has a stake, flies A320s and A319s with IAE engines. AirAsia’s fleet mostly comprises of the A320-216 (CFM56-5B6 powered).

The low thrust of the CFM56-5B6 translates to maintenance savings. Although CFM has more than 55% of the classic engine market that powers the A320 aircraft, it has a lower market share in Asia Pacific. In India, presently, 93 Airbus A320 family aircraft are powered by IAE Engines, while 66 are powered by CFM engines.

A320-111: No winglets, lower MTOW and range, CFM56-5A1 engines
A320-211: CFM56-5A1
A320-212: CFM56-5A3
A320-214: CFM56-5B4 (-5B4/P, -5B4/2, or -5B4/2P)
A320-216: CFM56-5B6

Those Airbus guys are also superstitious, as we can see, the last number is the engine last number, but the CFM56-5A3 is a A320-212, and not a A320-213.
The A320 -216 varriant is powerd by the CFM56-5B6 engine which has a total thrust of 23,500lbs.

There is quite a visual difference between the -211/-212 and -214/-216 in terms of Engines. The CFM56-5A has a longer spinner, but the CFM56-5B has a shorter one but with a longer casing and a 4-stage boster intake, which adds one more set of vanes compared to the CFM56-5A and makes the engine a bit bigger. On the outside, the engine is slightly larger, but once you look in the intake, youll notice right away.

The engine type has a history of cutting out in heavy rain / hail. It’s a bit eary to jump to conclusions but it sounds like the weather could have been a factor. Several fan blade failure incidents were experienced during the CFM56’s early service, including one failure that was noted as a cause of the Kegworth air disaster, while some variants of the engine experienced problems caused by flight through rain and hail. However, both these issues were resolved with engine modifications. Although the CFM56 is a very reliable engine there have been several engine failures throughout the life of the CFM56 family which were serious enough to either ground the fleet or require aspects of the engine to be redesigned. The engines have also suffered, periodically, from thrust instability events tentatively traced to Honeywell’s hydromechanical unit.

In 2002, Garuda Indonesia Flight 421 had to ditch into a river because of hail-induced engine flameouts, killing a flight attendant and injuring dozens of passengers. Prior to this accident, there were several other incidents of single or dual flameouts due to these weather conditions. After three incidents through 1998, CFMI made modifications to the engine to improve the way in which the engine handled hail ingestion. The major changes included a modification to the fan/booster splitter (making it more difficult for hail to be ingested by the core of the engine) and the use of an elliptical, rather than conical, spinner at the intake. While these changes did not prevent the 2002 accident, the investigation board found that the pilots did not follow the proper procedures for attempting to restart the engine, which contributed to the final result. Recommendations were made to better educate pilots on how to handle these conditions, as well as to revisit FAA rain and hail testing procedures.

One issue that led to accidents with the CFM56-3C engine was the failure of fan blades. This mode of failure led to the Kegworth air disaster in 1989, which killed 47 people and injured 74 more. After the fan blade failed, the pilots mistakenly shut down the wrong engine, resulting in the damaged engine failing completely when powered up after descent. Following the Kegworth accident, CFM56 engines fitted to a Dan-Air 737-400 and a British Midland 737-400 suffered fan blade failures under similar conditions, although neither incident resulted in a crash or injuries. After the second incident, the 737-400 fleet was grounded.

At the time it was not mandatory to flight test new variants of existing engines, and certification testing failed to reveal vibration modes that the fan experienced during the regularly performed power climbs at high altitude. Analysis revealed that the fan was being subjected to high-cycle fatigue stresses worse than expected and also more severe than tested for certification; these higher stresses caused the blade to fracture. Less than a month after grounding, the fleet was allowed to resume operations once the fan blades and fan disc were replaced and the electronic engine controls were modified to reduce maximum engine thrust to 22,000 lbf (98 kN) from 23,500 lbf (105 kN). The redesigned fan blades were installed on all CFM56-3C1 and CFM56-3B2 engines, including over 1,800 engines that had already been delivered to customers.

Airlines have reported 32 events involving sudden instability of thrust, at various points during flight, including high thrust settings during climb to altitude. The problem has been long-standing. In 1998, two 737 pilots reported that their engine throttles suddenly increased to full thrust during flight. A very recent investigation has led to the tentative conclusion that the problem originates in the Hydromechanical unit, and may involve an unacceptable level of fuel contamination (with water, or particulate matter, including biodegradables that create solid chunks in the fuel), or overuse of biocides to reduce bacterial growth. Boeing told Aviation Week and Space Technology that CFM International had revised its FADEC software. The new software reduces the duration and degree of thrust-instability events by cycling the fuel monitoring valve and the electrohydraulic servo unit to clean the EHSV spool. This software fix is not intended to be a definitive solution to the problem; however CFM claimed that no further reports have reached it after this change was made.

Dan Winther
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