Air carrier flight crew reported uncommanded go-around and loss of aircraft control while on approach into IND.
Synopsis
Air carrier flight crew reported uncommanded go-around and loss of aircraft control while on approach into IND.
Narrative
We were cleared for the ILS 32 into Indy. We intercepted the glide slope from beneath; and then as I was transitioning outside as the airfield was in sight; the aircraft initiated a go-around seemingly on its own after first trying to dive; then trying to overcorrect pitch. This placed the aircraft into a near stall condition on the autopilot (stall tape rapidly approaching the speed); so I disconnected the autopilot and flew manually on the go around (GA). I decided to continue the execution of the GA even though we would have had plenty of time to be stable; because I was unsure of why it had entered GA mode. My hands were on top of the thrust levers; and the First Officer (FO) also indicated he did not hit the TOGA button. We received no messages; aural alerts; and the stick shaker did not activate. We executed the go around and came around for another try. This time I had a suspicion that it was a false glide slope so I flew it manually using the VGSI and completed a safe landing. On the second approach; we noticed the glide go full deflection under us in about 1-2 seconds at around 2500 ft.; then immediately snap back in the vicinity of the flight path. We were following the VGSI this time outside; but I believe that may have been the cause of the first undesired state. We reported our observations to Tower and Ground. I don't recall noticing any vehicles or aircraft near the approach end.Suggestions: I'm not sure what we could have done differently. We followed our SOPs for setup; initiation; and conducting the approach. I did have to go against the SOP on following the Flight Director (FD) or pitching to 12 degrees as the stall tape was rapidly approaching the speed due to; essentially; G-loading. However; we did execute the SOP in effect; flying the airplane first and foremost.
Second reporter narrative
On Approach into IND shooting the ILS 32 I was pilot monitoring. Approach was normal and we were fully configured approaching the FAF at BTTLR. Autopilot and auto throttles were engaged. We were in approach mode with LOC and GS captured. At around 2500ft MSL glide slope was lost. The plane on autopilot initially pitched down to catch the glide slope then when it was fully gone a second later entered a go around mode. Neither I nor the Captain had hit the TOGA button to our knowledge. We hesitated for a second to try and perceive what the aircraft was doing without our input. The Captain then took manual control disengaging autopilot and calling for a go around. We began to clean up the aircraft with flaps 2 and toga set. I called Tower to let them know we were in a go around and they gave us a heading and altitude and asked for the reason. I omitted to call positive rate which consequently didn't get the Captains attention to call for gear up as he was busy hand flying. I was late to get the gear up but soon had the aircraft reconfigured to re shoot the ILS 32. We briefed the possibility of the automation losing the glide slope again and agreed if it occurred in the same spot to continue the approach hand flown. On the previous approach we had the runway in sight with the VGSI and felt safe to continue as it was VMC. On the second attempt we lost glide slope again in the same spot with the aircraft reacting the same way first attempting a pitch down motion to capture the glide slope loss. The glide slope then came back around 3 seconds later which I had not noticed on the first attempt; probably due to task saturation in the go around. The Captain immediately got autopilot (AP) off before a go around would be triggered and we continued on the approach with a normal landing. On the Ground frequency the Captain let ATC know we had twice lost the glide slope at 2500ft. Suggestions: Paying closer attention to my pilot monitoring duties I may have caught the glide slope loss sooner and called for the go around. This would have taken the surprise factor out and I could have reacted to the situation quicker.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.