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Supporting technical information A98H0003

Cabin safety

Cabin emergency preparation/Evacuation checklist

The Cabin emergency preparation/Evacuation checklist specifies the procedures for cabin crew to follow in the event of smoke or fire on board the aircraft. The procedures are as follows:

Reports of unusual smells

Unusual smells on HB-IWF on previous flights

HB-IWF operating as flight SR 178

Approximately three weeks before the accident, an unusual smell was detected by cabin and flight crew on HB-IWF (the occurrence aircraft) operating as SR 178 (Zurich to Hong Kong, China, to Manila, Phillippines), on 10 August 1998.

Prior to boarding the passengers in Zurich, the first-class galley F/A detected an unusual smell while working in the area of Flight Attendant Station 1.1.Footnote 1 Shortly thereafter, the M/Carrived and commented on the unusual smell. A second F/A working in the area also noticed the smell, as did one of the business-class cabin crew. The M/C walked through the entire aircraft cabin and confirmed that the smell was not present elsewhere in the cabin. Cabin crew described the smell as follows: something scorched or burnt, warm rubber, similar to an over-heated electrical appliance, or possibly, some type of gas or chemical with which they were unfamiliar. The smell was first detected when the forward cabin doors were open to facilitate catering. They speculated that perhaps the smell was coming from outside the aircraft. The smell persisted when the doors were closed. The ovens being used to warm the hot towels were checked, but there were no unusual smells. When the ovens were turned off, the smell remained. It was suggested, and the M/C agreed, that the flight crew should be informed of this abnormal condition.

The M/C asked an FO from the relief crew to investigate. The FO noted a very faint smell described as slightly acrid, similar to the smell produced when an electrical device is used for the first time. The M/C and the FO went to the cockpit and reported their observations to the captain. They checked the aircraft logbook to determine whether any electrical components in the first-class galley had recently been changed. There were no records of such a change. The captain sent a second FO from the relief crew to investigate. He too detected an unfamiliar but very faint smell. The flight crew concluded that the smell would not constitute a problem.

Shortly before the take-off roll, the first-class galley F/A and the M/C went to the cockpit and advised the captain that although its intensity fluctuated, the smell persisted. The captain was asked to come back to the cabin and assess the situation. The captain did so, and perceived a faint odour of warm plastic between the 1.1 flight attendant jump-seat and the garbage can that is near the edge of the cockpit door when the door is opened 90 degrees. He estimated that the smell was strongest approximately 1 m from the floor. He concluded that the smell was not strong enough to be of concern, did not warrant further investigation, and that the flight would depart as scheduled. The captain instructed the M/C to keep him apprised of the situation. The captain did not enter any information in the aircraft logbook regarding the unusual smell.

Cabin crew reported that the smell remained for the first six hours of flight, subsided, and reappeared one hour before landing. The smell was described as having been strongest during the final hour of flight. The cabin crew did not convey this information to the flight crew.

On arrival in Hong Kong, the flight crew and the cabin crew completed their duty day. During deplaning, a cabin crew member met the flying station maintenance engineer, who was providing the maintenance support for–and was scheduled to accompany the flight to–Manila, and told him about the unusual smell on board the aircraft. In response to this information the station engineer

As there was no recurrence of the smell, maintenance personnel did not make an entry in the aircraft logbook regarding the actions taken in relation to the reported smell.

Following the accident of SR 111, it was reported that during SR 179, all of the CBs had been in the normal position, that there were no unusual smells on board HB-IWF, and that no reports of any unusual smells during the flight from Hong Kong to Manila had been reported.

If there had been an entry in the aircraft logbook regarding the unusual smell, maintenance personnel would have been required to take further action (such as removing panels, including panels around the cabin door, removing the oven(s) and inspecting further in the area of Flight Attendant Station 1.1, or both).

Cabin flight report regarding unusual Smell on HB-IWF operating as SR 178

In August 1998, the M/C who had been on duty during the Zurich-to-Hong Kong leg of SR 178 filed a Cabin Flight Report describing the unusual smell detected on HB-IWF and requesting that the event be investigated.

Swissair's response to cabin flight report regarding unusual smell on SR 178

In response to the Cabin Flight Report, Swissair indicated that before take-off in Zurich the plane had been treated with a chemical disinfectant and that remnants of the disinfectant may have led to the smell. The aircraft had just completed a maintenance "A check" and that a chemical, an insecticide known as Ketometrin, was used during this check. SR 178 was the first flight following the "A check," which had been completed only hours before the flight.

Additional information

Following the accident, an interview questionnaire was distributed to approximately 500 flight and cabin crew to determine whether they had experienced any unusual event, including abnormal sounds, smells, or sights in HB-IWF. There were 432 responses received. Other than reports of the unusual smell (with no smoke) on SR 178 on 10 August 1998, there were no reports of unusual smells in the area noted above between August 10 and the occurrence. There were no reports of unusual smells recorded in aircraft records or mentioned during subsequent interviews with 36 flight and cabin crew members who had been aboard the aircraft, including the crew of SR 102, who flew HB-IWF on the flight before the accident flight.

HB-IWF flew 50 flights between August 10 and the occurrence without any known recurrence of the unusual smell.

Assessment of link between SR 178 and SR 111: HB-IWF

As an unusual smell was reported on the accident aircraft (as Flight SR 178, 10 August 1998) approximately three weeks before the accident, investigators assessed any potential link between that unusual smell and the events on the accident flight.

Unusual smell on another Swissair MD-11: HB-IWH

On two occasions a "burnt" or "burning" odour was detected on another Swissair MD-11 aircraft: HB-IWH.

11 July 1998

On 11 July 1998, a passenger on board HB-IWH operating as SR 111 detected a "strong, nasty odour of something burning. It was not a kitchen smell, but rather something which should not burn." The smell was detected in flight, after meal service, in the area of Passenger Seat 14H. The passenger did not report the unusual smell to the cabin crew during or immediately following the flight.Footnote 2 There is no record of anyone else detecting an unusual smell on that flight.

18 August 1998

On 18 August 1998, a passenger on board HB-IWH operating as SR 264 detected an unusual smell, described as a burnt odour. The smell was detected prior to take-off in the mid-cabin area at Seat 18J. The passenger, who identified himself as an aircraft maintenance engineer for a major airline, was very concerned and reported the abnormal condition to an F/A. The F/A also smelled a burnt odour and reported the abnormal condition to the flight crew and the M/C. The M/C investigated, but did not smell anything. He reported this to the flight crew. The F/A reported that maintenance personnel boarded the aircraft, adjusted "a nozzle," and advised that the smell would disappear in flight, which it did.

Neither the F/A nor the M/C completed a Cabin Flight Report concerning the burnt odour. The captain did not make an entry in the aircraft logbook regarding the burnt odour. There were no entries in the aircraft logbook by maintenance personnel to indicate either who had been on board the aircraft or what actions were taken. It could not be determined who had requested maintenance services.

After learning of the SR 111 accident, an F/A from SR 264 contacted Swissair officials in Zurich to report her recent experience on an MD-11 aircraft. Because the F/A did not know the registration of the aircraft used for SR 264, she was concerned that it might have been the same aircraft as that of SR 111 (HB-IWF). It was not.

Assessment of the link between unusual smells on HB-IWH

Given that the same aircraft, HB-IWH, was used for both flights and that on each flight, passengers reported a burnt odour within an area spanning four passenger-seat rows (at passenger seats 14H and 18J, respectively), investigators assessed any potential link between SR 111 (July 1998) and SR 264.

However, because there are no records or other information indicating the source of the burnt odour on SR 264, and because the passenger from SR 111 (July 1998) only reported the burning smell to the TSB several months after the flight, it was not possible to draw any link between the two events.

Reporting and recording of abnormal conditions

Procedures for cabin crew

The Cabin Emergency Manual, Chapter 2.1, "Standard Emergency Procedures," Section 1, General, states that "any abnormal condition, e.g., an explosive or other unusual noise, fire or smoke, must be reported immediately to the commander by the cabin crew member who observed it." An unusual smell is considered an abnormal condition. At the time of the occurrence there was no requirement to record abnormal conditions or perceived unsafe conditions in the cabin logbook. Typically, only technical deficiencies concerning the cabin and the galley were entered in the cabin logbook by the M/C. The cabin logbook would then be presented to the cockpit crew at least 30 minutes prior to landing, at which time the original copy of any entries made were given to the captain, who would subsequently transcribe them into the aircraft logbook.

The reporting of abnormal conditions or perceived unsafe conditions is also addressed in the General Basics Cabin Crew Manual, Chapter 4.1, "Crew Regulations," Section 2, General, Subsection 2.3, Reporting, as follows:

[A]ll flight personnel shall report any details, in general or particular, which are considered to be unsafe…. Information about such incidents should be…forwarded via the established company channels…. Remember that non-reporting may be detrimental to safety.

Additionally, crew members can report any safety-related information through established confidential channels in Swissair.

Procedures regarding recording of "messages about irregularities of any kind" are contained in the General Basics Cabin Crew Manual, Chapter 4.1, "Crew Regulations," Section 3.2, Cabin Crew Reports. Two types of cabin crew reports are cited: the Quick Report, which addresses service irregularities; and the Cabin Flight Report, which "is to be used for all problems which may not be dealt with on the Quick Report." The messages in these reports are categorized by subject and stored in a data bank.

A search of the MD-11 Cabin Flight Report database for additional information concerning abnormal smells on board HB-IWF or other MD-11 aircraft since 1997 resulted in only one other report. This report, dated 8 February 1998, concerned a broken reading light in C-class on board HB-IWA. The M/C reported that the CB was pushed twice and a noise and a smell of smoke were noted.

Cabin crew procedures for reporting and recording abnormal, perceived unsafe conditions, or both are similar for Canadian and United States air carriers. Cabin crew must immediately make a verbal report to the cockpit of any abnormal condition and must complete a written report (often referred to as an In-flight Incident Report).

Procedures for flight crew

At the time of the occurrence, it was normal practice for one or more members of the flight crew to investigate an abnormal condition reported by a cabin crew member. Subsequently, it was the captain's responsibility to determine whether the abnormal condition constituted a risk to flight safety. The captain would decide whether additional investigation, remedial action, or both were required; when it was to be done; and by whom. If the captain determined that the abnormal condition should be reported to maintenance, an entry was made in the aircraft logbook. If not, no entry was made in the logbook. There was no requirement that the flight crew report every abnormal condition or perceived unsafe condition to maintenance personnel; therefore, there was no automatic requirement for an entry to be made in the aircraft logbook.

Procedures for maintenance crew

Maintenance personnel must respond to any entry in the aircraft logbook, including entries regarding an abnormal condition, such as an unusual smell. Maintenance personnel must then make a corresponding entry in the aircraft logbook, reporting and recording what rectification action was taken, by whom, and when.

Maintenance crew were not required to take action in response to information conveyed informally during conversation with a crew member. If maintenance personnel did respond to such information, there was no requirement to make a subsequent entry in the aircraft logbook.


Cabin crew procedures clearly defined what constituted an abnormal condition. Procedures for reporting such abnormal conditions to the flight crew were clear and concise. These procedures appeared to have been consistently followed by members of the cabin crew.

Cabin crew procedures for recording such abnormal conditions did not state clearly when a written Cabin Flight Report was required. It was left to the discretion of the F/A whether the abnormal condition was "considered to be unsafe." What one F/A considered to be an unsafe condition might not be considered unsafe by another F/A. Given these procedures, the number of Cabin Flight Reports submitted, and the subjects they addressed, may not have accurately represented the presence of abnormal conditions within the system.

At the time of the occurrence, the flight crew procedures regarding the recording of abnormal conditions reported to them by cabin crew allowed for discretion by the flight crew. Abnormal conditions would have been recorded in the aircraft logbook at the captain's discretion.

Reporting and recording of abnormal conditions by SR 178 crew

Because the M/C of SR 178 considered the unusual smell an abnormal or suspicious condition, he submitted a Cabin Flight Report regarding the abnormal condition, as per procedure. Reporting of the abnormal condition was at the discretion of the flight crew; had the M/C not submitted a Cabin Flight Report, no record of any abnormal condition would have existed.

Reporting and recording of abnormal conditions by SR 264 Crew

The SR 264 cabin crew reported an abnormal condition, specifically a burnt odour, detected on board the aircraft to the flight crew as per procedure. In light of the fact that the burnt odour went away following take-off, neither the F/A who initially reported the smell nor the M/C considered the burnt odour to have been an unsafe condition. Therefore, neither submitted a Cabin Flight Report, nor were they required to do so. At his discretion, the captain made no entry in the aircraft logbook regarding the burnt odour. Had the F/A involved not called Swissair following the accident of SR 111, there would have been no record of a burnt odour on a second MD-11 aircraft.