Narrative:

On ILS runway 4 approach into ZZZ the captain's radio altimeter showed a yellow 'radio altimeter comparator' light flashing. The first officer had a red radio altimeter flashing light. I'm not sure what type of red radio altimeter light it was. The QRH instructs the pilot with working instruments to fly. I continued as PF. We had received a good ILS identify on both sides prior to the approach. As we were cleared for the approach; the localizer captured. We were above the GS descending but the GS showed us high by full scale to the bottom; indicating to us; the aircraft was high. (In retrospect; I am not sure that was a correct reading.) at that point; tower cleared us to land. We tried to descend as soon as possible to catch the GS. The GS started to move off the bottom of the scale. At about DOT from capturing; the GS just shot to the top of the scale and then back to the bottom several times. I asked the first officer to switch his side to VOR to get the DME. I think that was around 5-7 mi. I got intermittent GS fail flags. At approximately 3 mi we went around. Again; the GS was all over the place with same fail flags. Additionally; in the go around and level off; we were both getting intermittent navigation fail lights. Both the VOR and ILS were getting good idents all the time. I decided to exercise the captain's emergency authority/authorized and return to ZZZ. We switched to autoplt #2 and the first officer flew ILS with GS into ZZZ while I was on VOR with DME. Just prior to initial approach into ZZZ; we went through what other aircraft and ATC called moderate to heavy rain and some moderate turbulence. After speaking with maintenance; we suspected a lightning strike or static discharge. We had 9000 pounds of fuel.

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Original NASA ASRS Text

Title: AN MD80 CREW SUSPECTS A LIGHTNING STRIKE CAUSED A RADIO ALT FAULT AND ILS GS ERRORS CAUSING THEM TO GAR FOR ANOTHER APCH WITH DIFFERENT RADIOS.

Narrative: ON ILS RWY 4 APCH INTO ZZZ THE CAPT'S RADIO ALTIMETER SHOWED A YELLOW 'RADIO ALTIMETER COMPARATOR' LIGHT FLASHING. THE FO HAD A RED RADIO ALTIMETER FLASHING LIGHT. I'M NOT SURE WHAT TYPE OF RED RADIO ALTIMETER LIGHT IT WAS. THE QRH INSTRUCTS THE PLT WITH WORKING INSTS TO FLY. I CONTINUED AS PF. WE HAD RECEIVED A GOOD ILS IDENT ON BOTH SIDES PRIOR TO THE APCH. AS WE WERE CLRED FOR THE APCH; THE LOC CAPTURED. WE WERE ABOVE THE GS DSNDING BUT THE GS SHOWED US HIGH BY FULL SCALE TO THE BOTTOM; INDICATING TO US; THE ACFT WAS HIGH. (IN RETROSPECT; I AM NOT SURE THAT WAS A CORRECT READING.) AT THAT POINT; TWR CLRED US TO LAND. WE TRIED TO DSND ASAP TO CATCH THE GS. THE GS STARTED TO MOVE OFF THE BOTTOM OF THE SCALE. AT ABOUT DOT FROM CAPTURING; THE GS JUST SHOT TO THE TOP OF THE SCALE AND THEN BACK TO THE BOTTOM SEVERAL TIMES. I ASKED THE FO TO SWITCH HIS SIDE TO VOR TO GET THE DME. I THINK THAT WAS AROUND 5-7 MI. I GOT INTERMITTENT GS FAIL FLAGS. AT APPROX 3 MI WE WENT AROUND. AGAIN; THE GS WAS ALL OVER THE PLACE WITH SAME FAIL FLAGS. ADDITIONALLY; IN THE GAR AND LEVEL OFF; WE WERE BOTH GETTING INTERMITTENT NAV FAIL LIGHTS. BOTH THE VOR AND ILS WERE GETTING GOOD IDENTS ALL THE TIME. I DECIDED TO EXERCISE THE CAPT'S EMER AUTH AND RETURN TO ZZZ. WE SWITCHED TO AUTOPLT #2 AND THE FO FLEW ILS WITH GS INTO ZZZ WHILE I WAS ON VOR WITH DME. JUST PRIOR TO INITIAL APCH INTO ZZZ; WE WENT THROUGH WHAT OTHER ACFT AND ATC CALLED MODERATE TO HVY RAIN AND SOME MODERATE TURB. AFTER SPEAKING WITH MAINT; WE SUSPECTED A LIGHTNING STRIKE OR STATIC DISCHARGE. WE HAD 9000 LBS OF FUEL.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.