Jammed ailerons
It happened a long time ago but perhaps its worth relating.
I was flying a HS121 on a flight from UK to Helsinki one New Years Day There was little traffic about and we had been able to route from Heligoland Direct to the Outer Marker for Runway 22. This was quite a challenge in the days before GPS or INS just using NDBs. The temperature on the ground at Helsinki was -20C and cruise OAT -50C. We had left UK in rain. On disconecting the A/P on descent I found the ailerons totally imoveable. The first approach resulted in a go-around but the second was better and a normal landing made. You refresh your self on the secondary effects of rudder in a swept wing A/C