Sunday, March 31, 2013


(From Flight Safety Foundation)

Brief Description

Helios' Boeing 737-300 underwent maintenance on the night prior to the accident. The pressurization system was checked, but after completion of the tests the Pressurization Mode Selector (PMS) was reportedly left in the "Manual" position instead of the "Auto" mode. In manual mode the crew had to manually open or close the outflow valves in order to control the cabin pressure. The outflow valves were one-third in the open position which meant that the cabin would not pressurize after takeoff. The PMS mode was apparently not noted during the pre-departure checks by the crew.

In the morning the 737 was to operate Flight 522 from Larnaca to Prague, Czech Republic with an intermediate stop at Athens, Greece. The flight departed Larnaca at 09:07 for the leg to Athens with a planned flying time of 1 hour and 23 minutes. As the airplane climbed over the Mediterranean the cabin altitude alert horn sounded. This occurred as the 737 passed through an altitude of 10,000 feet. Cabin altitude is usually held around 8,000 feet. The crew possibly thought it was an erroneous takeoff configuration warning because the sound is identical. Then, at 14,000 feet, the oxygen masks automatically deployed and a master caution light illuminated in the cockpit. Because of a lack of cooling air another alarm activated, indicating a temperature warning for the avionics bay.

The German captain and the Cypriot co-pilot tried to solve the problem but encountered some problems communicating with each other. They contacted the Helios´ maintenance base to seek advice. The engineer told that they needed to pull the circuit breaker to turn off the alarm. The radio contact ended as the aircraft climbed through 28 900 ft. The circuit breaker was located in a cabinet behind the captain. The captain got up from his seat to look for the circuit breaker. The crews were not wearing their oxygen masks as their mindset and actions were determined by the preconception that the problems were not related to the lack of cabin pressure.

As the airplane was still climbing the lack of oxygen seriously impaired the flight crew. The captain probably became unconscious when he was trying to find the circuit breaker. The first officer was still in his seat when he also became unconscious. Because the plane's autopilot was programmed for FL340 the Boeing continued to climb until leveling out at that altitude some 19 minutes after takeoff. At 09:37 the 737 entered the Athens FIR but no R/T contact was established with the flight. Over Rodos at about 09:52 the airplane entered the UL995 airway. At 10:21 the airplane passed the KEA VOR, which is located about 28 nm south of the Athens airport. The airplane then passed the Athens Airport and subsequently entered the KEA VOR holding pattern at 10:38. All efforts by Greek air traffic controllers to contact the pilots were futile. Around 11:00 two Greek F-16 fighter planes were scrambled from the Néa Anghialos air base. At 11:24, during the sixth holding pattern, the F-16's intercepted the airliner. The F-16 pilots reported that they were not able to observe the captain, while the first officer seemed to be unconscious and slumped over the controls.
At 11:49, the F-16's reported a person not wearing an oxygen mask entering the cockpit and occupying the captain's seat. The F-16 pilot tried to attract his attention without success. At 11:50, the left engine flamed out due to fuel depletion and the aircraft started descending. At 11:54, two Mayday messages were recorded on the CVR. At 12:00, the right engine also flamed out at an altitude of approximately 7100 feet. The aircraft continued descending rapidly and impacted hilly terrain.

The same Boeing 737 had, suffered a loss of cabin pressure on December 20, 2004 during a flight from Warsaw to Larnaca. Three passengers needed medical treatment after landing in Larnaca. This incident was caused by a leaking door seal of the right hand rear door.

Direct Causes

1. Non-recognition that the cabin pressurization mode selector was in the MAN (manual) position during the performance of the:
a) Preflight procedure;
b) Before Start checklist; and
c) After Takeoff checklist.

2. Non-identification of the warnings and the reasons for the activation of the warnings (cabin altitude warning horn, passenger oxygen masks deployment indication, Master Caution), and continuation of the climb.

3. Incapacitation of the flight crew due to hypoxia, resulting in continuation of the flight via the flight management computer and the autopilot, depletion of the fuel and engine flameout, and impact of the aircraft with the ground.

Latent Causes

1. The Operator’s deficiencies in organization, quality management and safety culture, documented diachronically as findings in numerous audits.

2. The Regulatory Authority’s diachronic inadequate execution of its oversight responsibilities to ensure the safety of operations of the airlines under its supervision and its inadequate responses to findings of deficiencies documented in numerous audits.

3. Inadequate application of Crew Resource Management (CRM) principles by the flight crew.

4. Ineffectiveness and inadequacy of measures taken by the manufacturer in response to previous pressurization incidents in the particular type of aircraft, both with regard to modifications to aircraft systems as well as to guidance to the crews.

Contributing Factors to the Accident

1. Omission of returning the pressurization mode selector to AUTO after un-scheduled maintenance on the aircraft.

2. Lack of specific procedures (on an international basis) for cabin crew procedures to address the situation of loss of pressurization, passenger oxygen masks deployment, and continuation of the aircraft ascent (climb).

3. Ineffectiveness of international aviation authorities to enforce implementation of corrective action plans after relevant audits.

Wednesday, March 27, 2013


(From DGCA Accident Summary for year 2000)

Brief Description:            Boeing 737 aircraft VT-EGD, owned by Indian Airlines Ltd. and operated by Airlines Allied Services Ltd. took off from NSCBI Airport Kolkata at 0615 hrs on 17.07.2000 for Patna – Lucknow - Delhi. There were 58 persons on board, including six crewmembers. At approx 0713 hrs, the aircraft informed Patna ATC of the estimated arrival time at Patna as 0736 hrs. The aircraft informed Patna ATC at 0732 hrs that it would like to do a 360-degree due to being high on approach. The ATC informed the aircraft to report final for R/W 25 after carrying out a 360-degree turn and the pilot acknowledged the same. This was the last communication recorded between the aircraft and the ATC. During the approach for R/W 25 at Patna, the aircraft turned steeply to the left, losing height, and collided with the tree in the approach funnel and crashed in the Gardani Bagh area near Patna Airport. The aircraft was totally destroyed due impact with the ground and post impact fire.

The probable cause of the accident:       The cause of the accident was loss of control of the aircraft due Human Error (Aircrew). The crew had not followed the correct approach procedure, which resulted in the aircraft being high on approach. They kept the engines at idle thrust and allowed the air speed to reduce to a lower than normally permissible value on approach. They then maneuvered the aircraft with high pitch attitude and executed rapid roll reversals. This resulted in actuation of the stick shaker stall warning indicating an approaching stall. At this stage, the crew initiated a Go Around procedure instead of approach to Stall Recovery procedure resulting in an actual stall of the aircraft, loss of control and subsequent impact with the ground.

Factor: Pilot:      Non-adherence to standard operating procedure.