2023-01 · NASA ASRS report 1968148
A321 Flight Crew reported the failure of the #1 IRU after departure. #3 IRU was already on MEL. After running the checklists and QRH; the flight crew communicated with Dispatch. The decision was made to divert and land.
Flight departed ZZZ with #3 IRU inop per MEL XX-XX-G. During cruise flight at (estimated) XA45Z the autopilot disengaged because of a #1 IRU failure. This caused my attitude indications and nav indications to disappear from my display screens. I immediately transferred control of the aircraft to the First Officer who became the Flying Pilot for the remainder of the flight. I proceeded to perform the ECAM actions; which were minimal; other than noting failures and clearing the items on the ECAM display. The normal procedure for recovering flight instruments is to place the ATT HDG control on the Switching Panel to CAPT 3. But because the #3 IRU was inoperative; this action did nothing. After finishing the ECAM actions I advised ATC that we had a flight control problem and that we needed to descend to a lower altitude (to clear RVSM airspace) and that we would get back to them when able. We were given clearance to FL260 but decided to level at FL280 after it was offered by ATC. I was unable to contact Dispatch via the Crew Phone application on my iPad because I did not have WIFI capability. I assume this was because of the double IRU failure; but I have not confirmed this assumption. We were too far east of the ZZZ1 area Dispatch Direct VHF Network; so I spent a few minutes locating the appropriate communications frequency for our location in order to get a phone patch to the Flight Dispatcher. After explaining the situation to Dispatch; we decided that a diversion to ZZZ2 would be the safest course of action. We then advised ATC of our plan and proceed to ZZZ2 airport. As a result of the loss of 2 IRU units; the inoperative aircraft systems were Autopilot; Auto Thrust; Flight Directors; and Yaw Damper #1. The weather for the entire flight; from failure to landing; was VMC. We did not have navigation ability; so we were given radar vectors all the way to the localizer for Runway XXR at ZZZ2. We decided not to request priority handling for this situation as we felt the aircraft was fully controllable; the weather was good; and a normal landing was anticipated. The flight landed without further problems and proceeded to park normally at the assigned gate. An IRU failure on its own would not have caused any significant problems or the necessity to divert. However because of the inoperative #3 IRU; this became a much more problematic situation. I do not know the reason for the failure of the #1 IRU so I have no insight as to the causal factors beyond the application of an MEL to the #3 IRU. I believe this was a very rare occurrence. The failure of a second IRU unit is obviously considered a low probability event. Otherwise the MEL application would not be approved. I do not have any suggestions on how to prevent this type of event in the future.
IR3 was differed item before the flight; I checked the procedures during preflight and complied. We were cruising FL350; autopilot disconnected; initially I thought the Captain disconnected auto pilot inadvertently. Then Captain asked me what happened; from their question I realized it was a problem with the aircraft. I told him 'YOUR AIRPLANE' Captain replied back 'Your airplane I don't have instruments indications'. I took the airplane; and radios; I asked the Captain if I should request priority handling they replied no; not at this moment. I called ATC and I told them we had a problem with degraded flight controls; and no auto flight system; Controller asked me if I was requesting priority handling; I told ATC no; and that we were troubleshooting the problem and would keep them updated. I requested to descend to FL260 to leave RVSM airspace and it was approved; I also advised ATC that I might not be as accurate as the autopilot to maintain altitude and heading they replied it was not a problem; they were very helpful on the situation. On the Captain's side 'NO Quick Action; No ECAM Exemption; it was ECAM Action. I commanded ECAM ACTIONS.... Captain completed ECAM ACTIONS.IR3 was a deferred item in the MEL and we lost IR 1; having only IR 2 working only. The Captain briefed the Flight Attendants about the situation. Dispatch send us new paperwork for flying at FL260. The Captain checked the documents and told me we were good with fuel and weather to continue to ZZZ3; I suggested to deviate to ZZZ2 instead since it was closer and we could not take a chance; they considered my advice and agreed. They took the communications back and requested the deviation to ZZZ2; weather conditions were good; night time; some crosswind; I requested to get briefed on details of the approach; reviewed the status and requested vectors to land; at gear down aircraft entered in Direct; controls were a bit different as expected. The Captain backed me up during the approach regarding speed and vertical descend and a safe landing was conducted; with no further problems arrived to the gate; switched airplane and continued our trip to ZZZ3.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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