Date: 201602
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pneumatic Ducting
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: Pilot Not Flying; Captain
Anomaly: Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed As Precaution; Flight Crew Diverted; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: The climb-out was non-eventful. We reached our cruise altitude of 36;000 ft without any abnormal events or indications. Approximately 5 minutes after leveling off; the Master Warning indication illuminated; alerting us to a; 'Cabin Alt' issue. The Captain and I immediately donned our oxygen masks. Afterwards; the Captain initiated the checklist for; 'Cabin Alt/Rapid Depressurization.' During the process; the cabin altitude continued to climb.As the Captain was in the process of completing the Cabin Alt Checklist; the 'Cabin Oxygen On' annunciator illuminated. The cabin altitude continued to climb further. At approximately this time; the flight attendants chimed the cockpit. We told the flight attendants that the flight deck crew was ok; but that we were very busy and that we would give them more information shortly. We also instructed them to put on their oxygen masks. The cabin altitude was still uncontrollable after completing QRH procedures; therefore; as directed by that QRH; we decided to initiate the QRH procedure for; 'Rapid Descent.' The Captain coordinated the descent with ATC by asking for lower; and made them aware that we needed to descend urgently. As we were cleared lower; we began to initiate the rapid descent per the QRH. The Captain and I started to notice a strong burning smell as we were rapidly descending. The Captain opted to shut-off the left pac due to an abnormal indication. The right pack was showing the cabin supply temperature to be maxed out hot. The temperature selector on both packs was in the auto position; at approximately the 1 o'clock position prior to the Captain shutting the left pack off. We also noted that the right pac pressure was constantly 'bouncing' from zero to showing some pressure on the gauge. The flow light on the pressure control light was also constantly turning on and off. Immediately after the pack was shut off; the 'hot' smell began to diminish. As we leveled off at 10;000 feet from the rapid descent; neither pilot detected the unusual smell further.Due to the Rapid Depressurization and the unusual 'hot' smell; the Captain decided that the safest course of action would be to divert to the nearest suitable airport. I requested such an airport from ATC while the Captain attempted to reach company on Commercial Radio. ATC noted that the weather ahead near our route was not good. Visibility at most airports ahead; to the West; were approximately 1/4 mile. However; the weather behind us; to the East; was much better. ATC told us that the weather at ZZZ was 5 kt winds; 10 mi. visibility; and 6;000 ft. ceiling. ZZZ was approximately 70 miles away. We received clearance from ATC to proceed directly to ZZZ. I also requested to have ATC let our company know about the diversion; since the Captain was unable to reach them on ARINC. The Captain let the flight attendants know about our diversion; including the destination; and the approximate time to get there. The rest of the arrival was uneventful.The flight landed safely at ZZZ Airport. The flight crew was ok. The flight attendants noted that 2 of the passengers were a bit shaken up by the experience; but ok. Contract maintenance arrived at the aircraft about 20 minutes after parking at ZZZ. The mechanics were able to locate a chaffed tube in the tail section that they said was responsible for the depressurization. They explained that with the air conditioning tube disconnected; that the pressurized air in the cabin was able to escape into the tail compartment; depressurizing the aircraft. The damaged tube was deemed to be beyond repair by the contract maintenance team.The tube that caused the depressurization appeared to be in very poor condition. More frequent inspection/replacement of that part and the affected systems might have prevented the rapid depressurization/diversion event to occur.


Second narrative: This was the second leg of the day; the first being a flight that was diverted due to poor weather. The passengers on the diverted flight were given the option of taking a company provided bus to [their destination] or fly back. All but four passengers chose the bus option.The flight began normally and there were no issues during the taxi; take-off and climb phases. All indications were normal until approximately 5 minutes after reaching our cruise altitude of FL360. Without warning the Cabin Altitude aural warning sounded along with the associated master warning and Cabin Alt annunciator. I quickly glanced at the pressurization controller which confirmed the cabin altitude was at 10;000 ft. I donned my oxygen mask and instructed the first officer to do the same. I contacted ATC and requested a lower altitude. We were initially given a descent to FL320 and we quickly began the descent for a lower altitude. At this time I noted the right pack temperature valve showed the valve position to be in the full hot position with the temperature knob in the 1 o'clock position (Auto Mode). My initial thought at this point was that the right pack had over heated and shutdown and FL360 was too high of an altitude for the remaining pack to keep the cabin pressurized. Sustaining my thought process; I remembered an MD-80 a few months earlier that was having an issue with one of the packs going to full hot in auto mode and shutting down. In an attempt to confirm this was the problem; I cycled the right pack off and then back on. To my surprise; the indications I saw suggested the pack was operating normally and we were dealing with a different problem. I switched the outflow valve control wheel to manual and attempted to roll it full forward (Fully closed) but it was already there. I looked up at the cabin rate of climb needle to see it was pegged at the max climb rate. All together it had only been a few seconds since the first sign of a problem but we had already come to the realization a descent to 10;000 ft was our only option at this point. ATC was notified we had a pressurization issue and need to descend to 10;000 ft immediately. They quickly came back with a clearance to descent to 10;000 ft and the first officer increased the rate of descent to the maximum possible. I began running the QRH procedure for Cabin Alt/Rapid Depressurization/Descent. Soon after I started; the lead flight attendant called the flight deck and the first officer advised her of the problem. Once I completed the QRH procedures I contacted the flight attendants via interphone to ensure everyone was ok. To my surprise; she said none of them were wearing their oxygen masks. I told her that everyone needed to place their mask on immediately and we would notify them when it was safe to remove them. Upon reaching 10;000 ft I made a PA to inform everyone it was ok to remove their oxygen mask and we would be diverting to a nearby airport. We coordinated with ATC and decided to land at ZZZ. It was closest airport with acceptable weather conditions. I communicated this to the lead flight attendant and she advised everyone else in the cabin of our plans. The rest of the flight was uneventful.After landing; mechanics inspected the aircraft and found the right bleed air line running from the right pack to the cabin had split and come loose from the pack. The left pack was not inspected by them until 2 days later; when they confirmed that it was fluctuating on and off (As per my logbook entry) but were unable to determine the cause. The following four write-ups were made in the aircraft logbook.Approx. 5 minutes after reaching FL360; Cabin Alt master warning illuminated and cabin alt was confirmed to be 10;000 ft. Both packs were in Auto temp control at 1 o'clock position. Right pack valve showed full hot. QRH procedure for cabin Alt/Rapid Depressurization was followed but aircraft never re-pressurized. After initiating a descent and reaching 10;000ft; left pack pressure was fluctuating erratically and a burning smell was noted. Left pack was turned off for the duration of the flight and the smell cleared as soon as the pack was turned off. All cabin oxygen masks dropped from ceiling after losing cabin pressure.Cabin oxygen masks at seats 3 A/C/D/E/F; 25 D/E/F; 26 D/E/F; 33 A/C/D/E/F and all masks at front F.A. station were activated.I contacted Maintenance control and not only told them of the four write-ups but also gave multiple people a rundown of the events leading up to our landing at ZZZ. I feel the majority of things were handled as well as possible under the circumstances but a few things I would have liked to see differently include the following.Flight Attendants put oxygen masks on immediately until instructed by the flight deck that it is safe to remove them.With reference to item 1; I wish I made a quick call to the flight attendants or a PA stating the current situation we had and that oxygen masks should be worn until further advised. Although; this would be difficult to do any faster than I or the first officer had already communicated to the flight attendants.Even though I told multiple members of maintenance control the status of the aircraft and the events that took place on this flight; there seemed to be some misinterpretations of events and false expectations of broken items specifically it appeared maintenance control thought the left pack was still operating normally.


Synopsis: MD80 flight crew experienced a loss of cabin pressurization at FL360. After attempts to control pressurization manually are unsuccessful; a descent was initiated followed by a diversion to the nearest suitable airport. When the cabin oxygen masks dropped automatically; the flight attendants failed to put them on until instructed to do so by the Captain.