Aviation Investigation Report A98H0003
1.6.19 Emergency Equipment
- 22.214.171.124 - Cockpit Emergency Equipment
- 126.96.36.199 - Cabin Emergency Equipment
- 188.8.131.52 - Flight Crew Oxygen
- 184.108.40.206 - Passenger Oxygen
The Swissair configuration of the MD-11 cockpit has four seats, with an oxygen mask dedicated to each seat position (see Figure 17). A rechargeable flashlight for each pilot is readily available from the seated position. Additional emergency equipment is stored on the cockpit rear wall behind the captain's seat; to retrieve this equipment, pilots have to leave their seats. The additional equipment includes a Halon 1211 fire extinguisher, fire gloves, two sets of portable protective breathing equipment (PBE), two additional flashlights, a crash axe, four life vests, and an emergency VHF radio transceiver. The emergency transceiver, which is normally stowed in the OFF position, is self-contained, battery operated, and pre-set to the international emergency frequency 121.5 MHz.
The following emergency equipment is located in the cabin: seven fire extinguishers (five Halon 1211 and two dry chemical extinguishers) and fire glove sets, eight 310 litre (L) and two 120 L portable first-aid oxygen bottles (STI1-33) with masks, one crash axe, 14 flashlights, 11 sets of PBE, life vests for each passenger and flight attendant, medical kits, a megaphone, along with other miscellaneous items. In the skybunk flight crew rest areas there are two additional 120 L first-aid oxygen bottles, and two flashlights. In the cabin crew rest area there are an additional four 310 L oxygen bottles, one PBE, one Halon 1211 extinguisher, gloves, and a flashlight. (See also Section 220.127.116.11.)
18.104.22.168 Flight Crew Oxygen (STI1-34)
The Swissair MD-11 flight crew oxygen is supplied from one aluminum, high-pressure oxygen cylinder wrapped with a para-aramid fibre. The system delivers regulated oxygen through stainless steel lines to mask-mounted regulators, and supplies the captain, first officer, and the two observers' positions. A "T" fitting is installed in the stainless steel supply line near the crown of the aircraft, between STA 383 and STA 374, to provide an option for an additional crew mask in the freighter configuration. The "T" fitting is capped with an AN929-6 aluminum cap that, when installed, protrudes through the between-frame insulation blankets into the cockpit attic area (see Figure 5).
Each full-face mask assembly is stowed in a quick-access stowage box at each flight crew station, with the oxygen supply lines and microphone connections at the base of each stowage box (see Figure 11). When the oxygen mask stowage box door is opened, the mask microphone is automatically activated and the boom microphone deactivated.
The crew oxygen masks have a six-foot attachment line. Therefore, with the mask on, the captain can reach all of the emergency equipment, the cockpit door, and the overhead CB panels. The first officer would not be able to reach any of the emergency equipment, but can reach the cockpit door and the overhead CB panels. If conditions permitted, an option for the first officer would be to don an observer's oxygen mask; the hose length of either of these two oxygen masks would allow sufficient range of movement to reach the PBE and flashlights. The two portable PBEs each have a 15-minute supply of oxygen.
Each flight crew oxygen mask is fitted with a pneumatic harness, which is inflated by pressurized oxygen by manually actuating a lever on the regulator. When inflated, the harness allows easy donning and doffing of the mask, and fits easily over glasses and headsets. The harness deflates on release of the lever, tightening the mask to the wearer's face. The mask is equipped with a vent valve to purge any smoke from the goggles.
The mask-mounted regulators can function in one of three positions: normal diluter demand, 100 per cent oxygen, or emergency pressure breathing. The default position is normal diluter demand; 100 per cent oxygen or emergency pressure must be selected by the pilots. Such a selection would be made as warranted by the circumstances.
The SR 111 pilots were using oxygen for about 15 minutes. The charge state of the bottle at take-off was not determined; however, with both pilots using 100 per cent oxygen, the duration of the supply with a minimum dispatch pressure of 1 000 pounds per square inch (psi) would be at least 64 minutes. At 1 850 psi, which is a fully charged bottle, the duration would be about 119 minutes.
The crew oxygen cylinder pressure was last checked and the cylinder was refilled, on 9 August 1998, during an "A check." The cylinder was last hydrostatically tested on 17 March 1997. An examination of the crew oxygen cylinder showed that it was pressurized at the time of impact. During the time the CVR was recording, the pilots did not indicate having any problems with the oxygen system.
The MD-11 is fitted with independently mounted oxygen generators throughout the passenger and cabin crew areas. These generators supply oxygen masks that drop from compartments in the overhead panels. The masks are designed to be fitted over the nose and mouth. Once activated, each generator is capable of supplying a flow of oxygen to the masks that it serves for a minimum of 15 minutes.
The passenger cabin masks are stored behind module doors above the seats. The doors are held closed by electrically operated latches. The latches are powered by the 115 V AC buses 1, 2, and 3. If the cabin pressure decreases below a value equivalent to the standard pressure at 14 400 feet, the latches release and the doors fall open, allowing the masks to drop. The doors can also be selected open by the pilots through a switch in the cockpit.
The occurrence aircraft was equipped with 148 oxygen generators. (STI1-35) There were three sizes of oxygen generators installed; each served either two, three, or four masks. A total of 118 oxygen generators were recovered. Of the 83 examined in detail, (STI1-36) 53 were determined to have activated because of the impact. It was determined that none of the oxygen generators that were examined contributed to the fire, and that the passenger oxygen masks were not in use during the flight. (STI1-37)
The Swissair MD-11 Aircraft Operations Manual (AOM) warns that passenger oxygen masks must not be released below a cabin altitude of 14 000 feet when smoke or an abnormal heat source is present, as the oxygen may increase the possibility or severity of a cabin fire. As is typical with passenger oxygen masks in general use in transport category aircraft, the passenger masks in the MD-11 were designed to provide a mix of oxygen and ambient air. Therefore, the use of the masks would not have prevented passengers from inhaling smoke if it were present.
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