Baltic DH8D near Riga on Sep 9th 2012, loss of cabin pressure

An Air Baltic de Havilland Dash 8-400, registration YL-BAH performing flight BT-109 from Riga (Latvia) to Stockholm (Sweden) with 67 passengers and 4 crew, was climbing through 22,894 feet out of Riga when the crew received a "CABIN PRESSURE" warning indication, the cabin at that point indicated 8000 feet of altitude. The crew commenced a descent, when the cabin altitude reached 10,000 feet the flight crew donned their oxygen masks. Although the crew worked the relevant checklists and attempted manual and automatic control of cabin pressure, the cabin continued to climb until the aircraft had descended to 10,000 feet. The aircraft returned to Riga for a safe landing.

Latvia's Transport Accident and Incident Investigation Bureau (TAIIB) rated the occurrence a serious incident, conducted an investigation and released their final report concluding the causes of the serious incident were:

Proximate Cause

The source or origin of an event that caused this incident was the fact that the Pilot in Comand did not switch BLEED switches 1&2 on the Air Conditioning Control Panel.

Root Cause

The factor that resulted this incident was that the bleed airflow sources - both main engine bleed air systems which distribute the compressed air to the Environmental Control System and is also used for flight compartment and cabin pressurization were switched off and did not delivered flow of conditioned air through the Air Conditioning Unit (ACU).

Contributing causes

Indistinguishably to check visually, without finger touch, position of BLEED switches on the Air Condition Control panel on the OVERHEAD CONSOLE from LP seat position at night time.

Primary cause

The event after which incident became inevitable.

Performing by the crew in improper manner procedure “RAPID DEPRESSURIZATION/EMERGENCY DESCENT”, when warning “CABIN PRESS” came on, not corresponding to the requirements of Item 3.6.2.3. ”CABIN ALTITUDE WARNING” of OM Part B, Rev. 002 of 16.07.2012.

The TAIIB reported the captain (47, all necessary ratings valid, 7,121 hours total, 1,147 hours on type) was pilot flying, the first officer (32, all necessary ratings valid, 4,872 hours total, 991 hours on type) was pilot monitoring.

The flight data recorder showed both bleed air sources had been switched to OFF throughout the flight, the bleed valves therefore were off.

The TAIIB analysed that the checklists prior to engine start require the bleed air valves to be turned off. The aircraft departed in night time which made it difficult to see the position of the bleed air switches. Only the after engine start checklist required the bleed air switches to be turned on as required, the line up checklist required the bleed switches on/minimal and the after takeoff checklist required the bleed switches on/normal. The left hand pilot (pilot flying) was responsible to execute the checklists, however, the TAIIB stated: "Therefore, in opinion of investigation, it is not easy visually to check position of BLEED switches on the Air Condition Control panel located on right side of the OVERHEAD CONSOLE from LP seat position. BLEED switches did not switch on, during performing After Start, Line up and After take-off checklist. The position of BLEED switches was not checked by the finger touch. In opinion of investigation the checklists according to Chapter 2 of OM Part B 400, Rev 2 were performed carelesly by LP of crew. PF is responsible of performing after take-off checklist. PF after take-off was LP – Captain of aeroplane."

The TAIIB further analysed that when the cabin altitude rose to 10,000 feet the crew were required to perform the rapid depressurization/emergency descent checklist which again checked the position of the bleed switches. The TAIIB stated: "The crew did not perform “RAPID DEPRESSURIZATION/EMERGENCY DESCENT” procedure according to requirements of Item 3.6.2.3. CABIN ALTITUDE WARNING of OM Part B, Rev. 002 of 16.07.2012. As a result pressurization system did not operate at AUTO as MANUAL mode, because both engine bleed air systems were turned off."