Regional Jet 200 ER/LR (CRJ200)
Situational Awareness
Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft
This happened on the second-to-last flight of a four day trip while conducting initial IOE on First Officer (FO). I was pilot monitoring so to observe FO conduct a visual approach in preparation to complete that requirement for his IOE check-off. Just before the event occurred we were in communication with Approach and below 10;000 feet. We were given a clearance to fly direct to the FAF for the visual approach to Runway 4 while in a descent to 4;000 feet. At approximately 8;000 feet I elected to start the APU. This decision was made based on the realization it would be a very quick taxi to the terminal off the end of Runway 4; and we would need the 2 minutes of warm-up on the APU prior to landing; the 2 minute warm-up would be achieved by the time the After Landing Checklist would be completed and therefore the 10th stage bleed valve could be transferred to the APU in order to keep the cabin cool for deplaning once at the gate.While descending through 6;000 feet I began to notice a different smell; but it was very light and indistinguishable; it wasn't till after the event that I remembered noticing this. There was a FEW layer at 4;500 feet; which is also where a light haze layer began. After descending through this layer; I started to notice what seemed like a burning smell. However; I again dismissed the small assuming it was the remnant of a local fire on the ground (much like how you can smell a sewer or flatulence-like smell while descending into the lower haze layer into AGS; but in reality is the smell from the paper mill next to the airport... This can be as high as 4;000 feet).  In fact I remember surveying the local landscape for evidence of a fire; or at least one that had dissipated not long before our arrival in the area. We were then given a clearance to descend to 2;500 feet and it was after this when we heard a triple chime and 'APU; APU'. I immediately noticed that the APU EGT was in the red; and slowly climbing. In past experience there are times when this warning is expected momentarily; when transferring the 10th stage bleeds to the APU. However; there was no electrical or pneumatic load on the APU when this warning occurred. Furthermore; the EGT was increasing. At this moment I had reached for the QRH; but then we heard a single chime with the associated message of 'APU FIRE FAIL'.At this point; with the smell of something burning coming through the air conditioning system; the APU EGT in the red and climbing; and a faulty APU fire warning system; I elected to immediately shut the APU down. I first pushed the START/STOP button; and didn't wait to also hit the PWR/FUEL button.Shutting the APU down on the last 5 miles of the approach is what I felt was appropriate instead of running the QRH; in addition to the fact I had an inexperienced FO's at the controls who I needed to keep my attention on. In addition; if there was a fire; I wanted to get the aircraft on the ground ASAP so to evacuate if necessary to prevent any injury to passengers.After the APU was shut down I informed approach that we may have a possible APU fire and that we are [landing in emergency condition]. We were then handed off to tower control. As I checked-in with Tower; I requested that the fire trucks 'roll' so they could meet us at the runway.The final approach and landing was conducted by the FO in a normal manner and we brought the aircraft to a complete stop. I requested to communicate with the fire trucks on ground control. Once on frequency and in contact with the fire trucks; I requested a thermal scan of the aft of the aircraft for any signs of a fire. They replied that there was no sign of a fire. I therefore requested a taxi to the gate and that the fire trucks trail behind. We were given the clearance and proceeded to the gate and parked without further incident. After opening the door PA announcement was made by myself to explain what happened to the passengers and to apologize for any excitement that may havebeen caused. All deplaned in a normal and calm manner.Once on ground power; we shut the right (and final) engine down; completed the checklists; and then I proceeded to coordinate with the fire chief and emergency response outside the aircraft while FO contacted the company and remained on the flight deck for any assistance needed from that position. Three indicators occurred within the same time frame that led me to conclude there was a possible and real threat of an APU fire. These indicators include: smell of burning or hot friction from the air conditioning system; APU OVERHEAT red warning message with the EGT in the red and increasing steadily; and APU FIRE FAIL caution message.
CRJ200 Captain experiences a possible APU fire in flight after attempting to start the APU prior to landing. APU EGT is detected in the red and climbing followed shortly by an 'APU FIRE FAIL'. The APU is shut down and the Tower is advised of the possible fire.