Air carrier flight crew reports coupled approach to Runway 10 at SBLG that would have resulted in touchdown to the left of the runway had the crew not intervened. Indications in the cockpit were normal and steady; leading the reporter to believe the LOC may be misaligned.

Narrative

We planned and briefed to do an autoland on Runway 10 at SBGL due to possibly deteriorating visibility. ATC was notified on our intentions and was unresponsive. Visibility was actually several KM with haze and fog over the water. At approximately one mile; with all tracking parameters met; winds very light and aircraft looked on certerline; at 1/2 mile aircraft was visually slightly left on runway centerline; yet localizer and glideslope tracking were perfect in the cockpit. At 100 FT aircraft was close to the edge of the left side of the runway. At approximately 60 FT I disconnected the autopilot and made a smooth uneventful transition to the centerline and landed. If allowed to continue; the landing looked as if it would be so close to edge of the runway that the left main gear would be in the grass. Again all tracking parameters appeared perfect. No NOTAM's were in effect that were related to the ILS for Runway 10 and this is a CAT II runway. All aircraft tracking and performance was perfect. This ILS was probably unprotected; but it's signal appeared consistent (no minor aircraft deviation or 'jerkiness'). ILS may be misaligned. Coupled landing would have been unsafe.