ASN Aircraft accident Boeing 737-31S 5B-DBY Grammatikos
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Status:Accident investigation report completed and information captured
Date:Sunday 14 August 2005
Type:Silhouette image of generic B733 model; specific model in this crash may look slightly different
Boeing 737-31S
Operator:Helios Airways
Registration: 5B-DBY
MSN: 29099/2982
First flight: 1997-12-27 (7 years 8 months)
Total airframe hrs:17900
Engines: 2 CFMI CFM56-3C1
Crew:Fatalities: 6 / Occupants: 6
Passengers:Fatalities: 115 / Occupants: 115
Total:Fatalities: 121 / Occupants: 121
Aircraft damage: Destroyed
Aircraft fate: Written off (damaged beyond repair)
Location:2 km (1.3 mls) from Grammatikos (   Greece)
Phase: En route (ENR)
Nature:International Scheduled Passenger
Departure airport:Larnaca Airport (LCA/LCLK), Cyprus
Destination airport:Athens-Elefthérios Venizélos International Airport (ATH/LGAV), Greece
Flightnumber: 522
Helios' Boeing 737-300 5B-DBY 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 crew 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 not 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, 5B-DBY, 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.

Probable Cause:

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.
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.
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.

Accident investigation:

Investigating agency: AAIASB Greece
Status: Investigation completed
Duration: 1 year and 2 months
Accident number: 11/2006
Download report: Final report


Flightcrew incapacitation
Loss of control

» SKYbrary 
» Air Safety Week, August 29, 2005
» Air Safety Week, Sept 26, 2005
» Crashed Helios 737 ran out of fuel / David Learmount. - Flight International 23/08/05
» Crew confusion found in Athens plane crash / Don Phillips. - International Herald Tribune 7/9/2005
» Helios probe reveals similar cases / David Learmount. - Flight International 15/11/05
» Hellenic Ministry of Transport
» Athens News Agency, ERT, CNN

Follow-up / safety actions

AAIASB issued 16 Safety Recommendations
FAA issued 2 Airworthiness Directives

Show all...


photo of Boeing-737-31S-5B-DBY
accident date: 14-08-2005
type: Boeing 737-31S
registration: 5B-DBY
photo of Boeing-737-31S-5B-DBY
accident date: 14-08-2005
type: Boeing 737-31S
registration: 5B-DBY
photo of Boeing-737-31S-5B-DBY
accident date: 14-08-2005
type: Boeing 737-31S
registration: 5B-DBY
photo of Boeing-737-31S-5B-DBY
accident date: 14-08-2005
type: Boeing 737-31S
registration: 5B-DBY
photo of Boeing-737-31S-5B-DBY
accident date: 14-08-2005
type: Boeing 737-31S
registration: 5B-DBY
photo of Boeing-737-31S-5B-DBY
accident date: 14-08-2005
type: Boeing 737-31S
registration: 5B-DBY
photo of Boeing-737-31S-5B-DBY
accident date: 14-08-2005
type: Boeing 737-31S
registration: 5B-DBY
photo of Boeing-737-31S-5B-DBY
accident date: 14-08-2005
type: Boeing 737-31S
registration: 5B-DBY
photo of Boeing-737-31S-D-ADBQ
accident date: 14-08-2005
type: Boeing 737-31S
registration: D-ADBQ
photo of Boeing-737-31S-5B-DBY
accident date: 14-08-2005
type: Boeing 737-31S
registration: 5B-DBY

Aircraft history
date registration operator remarks
29 DEC 1997 D-ADBQ Deutsche BA
13 MAR 2002 D-ADBQ DBA airline renamed
16 APR 2004 5B-DBY Helios Airways leased

This map shows the airport of departure and the intended destination of the flight. The line between the airports does not display the exact flight path.
Distance from Larnaca Airport to Athens-Elefthérios Venizélos International Airport as the crow flies is 924 km (578 miles).
Accident location: Exact; as reported in the official accident report.

This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
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