B350 CREW HAD THE LNDG GEAR NOT SHOW DOWN AND LOCKED WHEN THE GEAR WAS EXTENDED AT PTK.

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WHILE EXECUTING THE ILS RWY 9R AT OAKLAND COUNTY INTL (PTK); THE LNDG GEAR FAILED TO EXTEND WHEN THE CAPT SELECTED IT DOWN. THE CAPT GAVE CTL OF THE ACFT OVER TO ME IN ORDER TO TROUBLESHOOT THE PROB. DUE TO THE NATURE OF THE MALFUNCTION AND LOCATION ON THE APCH (INSIDE THE OM); I ELECTED TO EXECUTE A MISSED APCH. AFTER THE ACFT WAS ESTABLISHED IN A CLB; THE CAPT REASSUMED CTL OF THE ACFT. ATC ASSIGNED AN INITIAL ALT OF 3000 FT AND A HDG OF 090 DEGS. THE CAPT COMPLIED WITH THESE INSTRUCTIONS AS WE PROCEEDED TO COMPLETE THE MANUAL GEAR EXTENSION CHKLIST; WHILE BEING VECTORED FOR ANOTHER ILS RWY 9R AT PTK. ATC ALSO ASSIGNED US AN AIRSPD OF 170 KIAS. DURING THESE VECTORS; WE DEVIATED UP TO 200 FT HIGH OF OUR ASSIGNED ALT OF 3000 FT AND -20 KIAS OF OUR ASSIGNED SPD OF 170 KTS. ATC ADVISED US OF TFC OVERHEAD OF US AT 4000 FT; AND TO MAINTAIN 3000 FT. LATER IN THE VECTORS; ATC ASKED US TO STATE OUR AIRSPD. WE REPLIED THAT IT AS 150 KIAS. ATC ASKED US NOT TO LET IT 'GET ANY LOWER THAN THAT;' WHICH WE DIDN'T. THE CAPT INCREASED OUR SPD BACK UP TO 170 KTS UNTIL THE OM AND COMPLETED A NORMAL APCH. I BELIEVE THAT THE PREOCCUPATION WITH THE LNDG GEAR MALFUNCTION AND MANUAL GEAR EXTENSION WAS THE PRIMARY CAUSE OF THE ALT AND AIRSPD DEVS. THE DETERIORATING WX ALSO ADDED ANXIETY TO THE SIT; TAKING OUR ATTN OFF OUR BASIC INST SCAN. IN THE FUTURE; I BELIEVE THE AUTOPLT SHOULD BE USED; IF AVAILABLE; TO ALLOW THE PLTS TO REDUCE THEIR WORKLOAD DURING THIS TYPE OF MALFUNCTION. HOWEVER; ONE PLT NEEDS TO MONITOR THE AUTOPLT THROUGHOUT THE PROC TO ENSURE THE SAFETY OF FLT.