ALTDEV; ALT EXCURSION OCCURS WHEN DC9-30 FLT CREW BECOMES DISTR WITH TFC; RWY CHANGE; LCL WX; ACFT CONFIGN; FALSE WARNINGS AND ACFT EQUIP PROBS ON APCH TO RWY 27L AT DTW; MI.

Narrative

APCHED DTW FROM CLT VIA THE CETUS-2 ARR; BUT WAS VECTORED OFF THE ARR ROUTING TO A POS NE OF CETUS AND TOLD TO DSND TO 11000 FT; VICE THE NORMAL 12000 FT. WE WERE GIVEN TFC INFO FOR AN ACFT AT 12000 FT WHO WAS ON THE STANDARD CETUS GND TRACK; BUT NEVER SAW HIM. WE DID RECEIVE NUMEROUS TA'S FOR TFC AT OUR 7 O'CLOCK POS; AND 1000 FT ABOVE US; WHICH WE ASSUMED WAS THE TFC FOR WHICH WE WERE TOLD TO LOOK. THE ACFT IN QUESTION SHADOWED US UNTIL WE WERE NW OF CETUS; WHEREUPON; WE WERE TOLD TO SLOW TO 190 KTS FROM OUR CRUISE SPD OF 290 KTS. THE MANDATED 190 KTS REQUIRED US TO SELECT SLATS AND FLAPS 5 DEGS DUE TO OUR WT (APPROX 92000 LBS). WHILE WE WERE AT 11000 FT AND 190 KTS; THE AFOREMENTIONED 12000 FT ACFT SPIT OUT IN FRONT OF US. ATIS HAD TOLD US TO EXPECT RWY 21L; BUT INITIAL CONTACT WITH APCH CTL (124.25) TOLD US TO EXPECT A VISUAL TO RWY 27L. WE SUSPECTED THIS WAS DUE TO A TSTM WHICH HAD DEVELOPED NE OF THE FIELD WHERE THE DOWNWIND FOR RWY 21L WOULD NORMALLY BE. THE APCH CTL FREQ (124.25) WAS VERY CONGESTED AND IT WAS DIFFICULT FOR ANYONE TO GET IN A XMISSION OTHER THAN TO RESPOND TO DIRECTIVES FROM THE APCH CTLR. THE SUDDEN USE OF RWY 27L FOR TFC APCHING FROM THE SE CREATED TIME AND SPACE COMPRESSION PROBS AND THE CTLR'S PLATE WAS VERY FULL. WE WERE STILL AT 11000 FT AND 190 KTS WHILE WITHIN 15 MI OF THE RWY ON A 327 DEG HDG. THE CTLR FINALLY GAVE US A TURN TO 060 DEGS AND A DSCNT TO 8000 FT. THE 060 DEG HDG AIMED US RIGHT AT THE PREVIOUSLY MENTIONED TSTM AND THE 8000 FT ALT PUT US WITHIN ITS VERT DEVELOPMENT AS WELL. FREQ CONGESTION MADE IT IMPOSSIBLE TO VOICE OUR CONCERNS WITHOUT STEPPING ON SOMEONE ELSE'S XMISSION. THE FO SLOWED THE ACFT TO GIVE US MORE TIME PRIOR TO ENCOUNTERING THE TSTM. THE DECELERATION REQUIRED A FLAP SETTING OF 15 DEGS WHICH THE FO CALLED FOR AND WHICH I SET. IT WAS AT THIS TIME THAT I NOTICED THE BLUE 'SLAT EXTEND' LIGHT WAS NOT ILLUMINATED. SHORTLY THEREAFTER; WE RECEIVED A 'WINDSHEAR FAIL' ANNUNCIATOR LIGHT. THE COMBINATION OF THE PROX TO THE TSTM (NOW WITHIN 2 MI); THE ABSENCE OF THE 'SLAT EXTEND' LIGHT AND THE PRESENCE OF A 'WINDSHEAR FAIL' ANNUNCIATOR LIGHT DISTRACTED US TO A POINT THAT WE NEGLECTED TO NOTICE WE WERE STILL IN AN INSIDIOUSLY SLOW DSCNT DOWN THROUGH 8000 FT. I NOTICED OUR ALTDEV AT 7800 FT AND THE FO MADE AN IMMEDIATE PWR APPLICATION AND RAISED THE PITCH. WE HAD A NEW STYLE DIGITAL ALTIMETER AND THE LOWEST READING I SAW WAS 7780 INCHES. THE FO CLAIMS TO HAVE SEEN APPROX 7680 FT. I ESTIMATE WE WERE BELOW 8000 FT FOR APPROX 15 SECONDS AT THE MOST. WE RECEIVED NO TA OR RA WARNINGS NOR ANY COMMENTS FROM THE CTLR OR ANY OTHER ACFT. WHILE THE FO WAS RECOVERING TO 8000 FT; I MADE A REQUEST TO THE CTLR FOR A LOWER ALT. AT THIS POINT; THE CTLR ADVISED US WE HAD ONLY BEEN CLRED DOWN TO 8000 FT. I ADMITTED OUR TEMPORARY DEV AND TOLD HER WE WERE DISTRACTED BY THE THUNDERHEAD FILLING OUR WINDSCREEN AND THE SCARLET GLOW SATURATING OUR RADAR SCREEN. SHE GAVE US A TURN TO 080 DEGS AND HANDED US OFF TO ANOTHER CTLR WITHOUT ANY FURTHER COMMENT. THE NEW CTLR GAVE US AN APPROX 230 DEG HDG AND A FURTHER DSCNT (APPROX 4000 FT) WHEREUPON WE MENTIONED WE HAD THE RWY IN SIGHT. THE CTLR THEN CLRED US FOR A VISUAL APCH TO RWY 27L. WHILE ON THE DOGLEG INTERCEPT TO FINAL FOR RWY 27L; WE EXPERIENCED AN UNWARRANTED STICK SHAKER AT 190 KTS; WITH FLAPS 15 DEGS; AT A MODEST ANGLE OF ATTACK AND AN APPROX 300 FPM DSCNT RATE. MODIFICATION TO OUR AIRSPD; DSCNT RATE AOA (ANGLE OF ATTACK) AND PWR SETTING FAILED TO STOP THE STICK SHAKER. I PULLED THE CIRCUIT BREAKERS ASSOCIATED WITH THE STICK SHAKER AND WE ELIMINATED THE DISTR.