A flight crew’s timely response to a loss of cabin pressurization or to smoke or fumes is critical and certainly not the time to discover that your supplemental oxygen system isn’t working. This BCA author conducted a search of 100 recent NASA Aviation Safety Reporting System (ASRS) records that were submitted in 2016 and 2017 involving incidents in which oxygen masks were employed. Of the total, 71 involved a loss of pressurization or suspected smoke or fumes. The good news is that in these instances, the supplemental oxygen systems worked correctly, allowing the flight crews to breathe as they got the aircraft and their passengers safely on the ground.

However, the other 29 instances should cause concern as they bring attention to the serious risk posed for a flight crew being without supplemental oxygen as well as other serious problems with mask use when needed. One might think that supplemental O2systems are relatively simple, comprising few moving parts, and thus not prone to mechanical failures. Such systems should have 100% reliability, since they can be physiologically vital when put to use. However, the ASRS reports reveal a disturbing number of instances that challenge this perception.

Eight of the reports involved flight crews whose oxygen masks or hoses physically failed. “In cruise flight, I went to put on quick-donning mask as first officer was going to leave the flight deck for physiological needs. I pulled the mask out of the box and it came apart in my hands. It was useless had there been an emergency. Where the hose attaches with the microphone to the main rubber face area was broken and dangling. The full mask section was intact but the hose/microphone area was detached and hanging by a wire, no ability to breathe oxygen from the mask.” (NASA ASRS Report 1498858, November 2017)

A disintegrating mask is shocking enough, but let’s puts this into further perspective. These incidents could have turned into possible crew incapacitation and hull loss scenarios had the pressurization system malfunctioned or smoke/fumes started in the cockpit. A review of the ASRS system found other instances in which critical components failed. (See “Weak Points” sidebar.)

And another. “While out on the lavatory break, I heard a loud whoosh noise from up in the flight deck. This noise caught my attention so I immediately called up to the flight deck to request entry back in. When I got back into my seat the captain was holding the oxygen hose and his mask together in his hands while we could hear a hissing sound. The captain explained that the oxygen hose for his crew mask would not stay attached to the mask. . . . I then took hold of the mask and the oxygen hose and attempted to hold them together to save as much crew oxygen as we could. . . .The captain made several attempts at re-securing the oxygen hose to the mask but did not succeed. . . . Due to the positive pressure of oxygen coming from the hose, we were both unsuccessful at securing the oxygen hose. After several minutes we became unable to even hold the oxygen hose to the mask. At this point there was nothing to even slow the flow of the crew oxygen and we began to lose crew oxygen at an extremely fast rate.” (NASA ASRS Report 1462284, July 2017)

Similar reports revealed a cascading set of errors due to multitasking as the flight crews immediately started unplanned priority descents while troubleshooting the oxygen problem. These crews were stymied trying to find sections in their QRH addressing oxygen mask malfunctions or oxygen tube leaks, while confronting an abnormal failure that they’d never experienced in their simulator sessions. Furthermore, the decision making for an unplanned rerouting is considerable. With flight at a lower altitude, the increased rate of fuel consumption becomes a significant concern. Getting information for possible alternatives is not easy to do while in flight. Finding airports with suitable weather, approach minimums and runway lengths requires attention and focus. Runway surface conditions and applicable NOTAMs are equally deserving of careful attention. Under these multitasking conditions, it is understandable that flight crews forget to do the descent checklist or approach checklists.

A couple of the flight crews remembered after the incident that their aircraft had a walk-around oxygen bottle that would have been useful as a backup. Understandably in the stress of the situation that option had not seemed obvious at the time. Their ASRS reports serve as a valuable set of lessons for the rest of us.

Even though the aircraft pressurization systems remained working in these reported instances, a malfunction of the supplemental oxygen system warrants taking immediate action since it puts the aircraft in a precarious condition. One errant spark in a cockpit filling with 100% oxygen, or smoke and fumes, or a loss of pressurization could result in the loss of that aircraft and its occupants. Under such circumstances, the pilots need to descend to a physiologically survivable environment without delay.

An electrical spark in the presence of the supplemental oxygen system turned the flight deck of an EgyptAir Boeing 777-200 into a conflagration on July 29, 2011, at Cairo International Airport (CAI). The captain attempted to extinguish the fire with the cockpit fire extinguisher but was unsuccessful. Fortunately, the aircraft was on the ground at the time. The captain ordered an emergency evacuation and all passengers and crewmembers were able to escape without serious injury.

Due to the growing fire in the cockpit the first officer was unable to use a radio to summon emergency services. So, after exiting the Boeing he stopped a car on a service road to call the fire department. In case you were wondering, yes, the F/O had performed a test of the oxygen mask’s function during the standard preflight checklist. This took place approximately 30 min. before the fire erupted.

The cause of the ignition was later determined to have been an electrical fault in the F/O’s supplemental oxygen port. This resulted in electrical heating of the flexible hoses in the flight crew oxygen system, and the fire was subsequently fueled by a constant flow of oxygen. The cockpit was extensively damaged, and two holes were burned through the exterior skin under the F/O’s windows. The 777 was damaged beyond repair and written off.

During the investigation it was determined that the wiring to the F/O’s oxygen mask light plate had a missing wire clamp, the wiring was not sleeved, and a large loop of unsupported wire was found. Boeing issued a Service Bulletin in October 2011 recommending the inspection of the oxygen light plate wiring and, if necessary, installation of sleeving and replacement of damaged wires.

The NTSB is concerned that pilots using oxygen mask/goggle sets on FAR Part 121, 135 and 91 Subpart K flights may not be adequately trained to operate them if a smoke, fire or fumes event occurs. This should also concern flight crews of Part 91 aircraft.

On Sept. 3, 2010, a UPS Boeing 747 departed Dubai International Airport (DXB) on a cargo flight to Cologne, Germany (CGN). Twenty minutes into the flight, at approximately 32,000 ft., the crew advised ATC that there was an indication of an onboard fire and declared an emergency. Both pilots had donned their oxygen masks approximately 90 sec. after the fire bell sounded. Less than 90 sec. later, the fire caused severe damage to the flight control system and filled the cockpit with continuous smoke.

During the emergency descent the cabin reached a pressure altitude of 21,000 ft., followed almost immediately by the rapid failure of the captain’s oxygen supply without any indication of trouble. He said, “I got no oxygen. I can’t breathe.”

Unbeknownst to the flight pilots, the fire had severely damaged many significant systems on the aircraft, including the crew supplementary oxygen system supply. The damage caused a cessation of oxygen flow to the captain’s mask and reduced capacity for the remainder of the flight to the F/O’s mask. The captain left his seat to obtain the portable oxygen bottle but did not return due to incapacitation from toxic gases. The F/O could not view outside the cockpit, or see the primary flight displays. The aircraft subsequently entered an uncontrolled descent into terrain, 9 nm southwest of DXB. Both pilots died in the crash.

During the investigation, investigators received comments from several UPS line pilots regarding pilot training on the use of the oxygen mask and goggle sets. They reported receiving little hands-on instruction for the actual use of the set and smoke vent, and what they did receive occurred during initial training for the aircraft in the form of computer-based text and images. They also stated that they were never taught about the relationship between the emergency selector on the regulator and the need to simultaneously open the smoke vent to clear contaminants from inside the goggles or how to locate the switches on the oxygen regulator after the oxygen mask was donned. Further, they were never required to practice these actions in the presence of an instructor or check airman.

During an inflight smoke, fire or fumes event, the flight crew has limited time to complete checklist items, attempt to suppress or extinguish the fire, and divert the airplane to a successful landing. Oxygen mask and goggle sets must be donned quickly and with the correct regulator settings so that fire suppression/extinguishing procedures can begin as soon as possible. Any delay in setting the switches could increase the risk of flight crew incapacitation and delay the start of the smoke, fire or fumes checklist.

Other accident investigations and numerous ASRS reports also reveal flight crew difficulties with communications while oxygen masks were donned, validating the NTSB’s concern and likely indicating that this is a widespread problem. For example, on July 20, 2009, United Airlines Flight 949 departed London Heathrow Airport (LHR) for Chicago O’Hare International Airport (KORD). At 37,000 ft. and about 200 mi. south-southwest of Keflavik, Iceland, the flight crew encountered smoke in the cockpit and diverted to Keflavik International Airport (KEF). During the event, the flight crewmembers donned their oxygen sets and attempted, with difficulty, to establish and maintain crew communications.

According to pilot statements provided to the Icelandic Aircraft Accident Investigation Board, the captain stated, “We struggled with the audio panels to communicate with the masks on.” He therefore removed the oxygen mask to communicate with the F/O and relief pilot in the cockpit. The F/O said, “The entire process of donning goggles, the use of the oxygen mask, pushing all the different buttons and toggles to communicate with all the people involved was very frustrating at times. Between the goggles scratching my glasses and the smoke film in front of them too, it was hard to see at times. Too many items have to come together for this setup to work.” And the pilot added that “crew communications with oxygen masks on was non-effective and increased crew workload significantly. It was made worse with three crewmembers plus ATC all trying to communicate.”

In response to these events the NTSB issued Safety Recommendation A-11-089, to require airline, charter and fractional operators “to include, during initial and recurrent training, aircraft-specific training on establishing and maintaining internal cockpit communications when the oxygen masks are donned.”

Ten of the 100 ASRS reports involved flight crews detecting deficiencies with the masks or oxygen system pressure during preflight. For example, one reporter stated, “After arriving to the aircraft, we began our preflight duties and flows. Upon checking my oxygen mask, I ran the oxygen via the test button for 5 sec. and made sure the microphone worked. However, I immediately saw the O2 psi go from 1,600 to 100 instantly and stay there . . . . I suspected the valve on the bottle itself was in the off position. I told the captain and he agreed. We made an electronic logbook write-up and backed it up with a call to maintenance. They came to the plane and the mechanic was shocked.” (NASA ASRS Report 1486360, October 2017)

Several design issues came to light during the investigation of the Learjet accident that killed golfer Payne Stewart in 1999. It turned out that in the Model 35/36, the oxygen bottle regulator/shutoff valve is located in the nose cone of the airplane and therefore inaccessible to flight crewmembers during flight. It was further discovered that pilots may have difficulty visually verifying the position of this valve during a preflight inspection because of the way it’s installed in the airplane. The Safety Board noted that it is critical that the valve position indicators are clearly visible and easily understandable during preflight.

Oxygen bottle supply pressure is indicated on a gauge in the cockpit of the Learjet 35/36. Since a visual check of the oxygen bottle supply may not provide information about the position of the oxygen bottle regulator/shutoff valve, the pilots’ only sure indication in the cockpit that the oxygen bottle regulator/shutoff valve is in the OFF position would be the failure of the oxygen mask to deliver oxygen.

A half dozen of the ASRS reports indicated difficulties with stowing oxygen masks after completing preflight checks. The pressure-demand masks must be properly stowed in their containers to qualify as quick-donning equipment. Each mask has two red harness inflation levers that, when squeezed, allow the mask to be removed from the storage box. Releasing the levers after placing the mask over the head fits it securely to the head and face. Yes, it can be a pain stowing the oxygen mask, but doing so correctly could help safely resolve a dangerous situation.

A few of the reports indicated concerns that frequent preflight inspections are causing undetected wear and tear on the mask and hose connections. The pilots expressed concern that some mask designs are not sturdy enough for repeated extraction and re-stowing. These reports were submitted by regional airline crews whose aircraft can be operated by a dozen different pilots within a handful of days, each necessitating a full inspection of the oxygen system during an aircraft acceptance check. In addition, the ASRS submitters were concerned that many of the facemasks are getting scratched to the point that they would be difficult to see through in a real event. (See “When Irish Eyes . . . ,” Cause & Circumstance, page 28.)

Incidentally, if your aircraft cabin has become cold-soaked, it may be necessary to warm the cabin sufficiently to ensure the proper deployment and operation of passenger oxygen masks. The Cessna Encore manual, for example, stipulates that cabin temperature must be held at or above 32F for a minimum of 15 min. prior to takeoff after a prolonged ground cold soak.

It is vital that all flight crewmembers personally preflight their oxygen equipment to ensure that the mask is functioning, fitted properly and connected to appropriate supply terminals, that the oxygen supply and pressure are adequate, and that the oxygen buttons are selected for optimum performance in case of emergency.

All pilots of high-performance aircraft should receive appropriate, hands-on instruction regarding the use of oxygen mask/goggle sets, including the regulator’s emergency selector and smoke goggle venting, and practice communications using the mask microphones during initial and recurrent training.

Knowing how to do that could save your life.

Author’s Acknowledgement: I want to acknowledge the contributions of Sean Hareland, Davis Kahler, Josh Proulx, Sam Robinson and Jakeb Williams, all aviation students at Westminster College, Salt Lake City, in the preparation of this article. Their assignment on system malfunctions led to the discovery of several ASRS reports involving oxygen mask malfunctions, which in turn helped inspire my in-depth search of the ASRS database on the subject and to produce this feature.