AN LJ25 CREW; DEPARTING KDEK; OVERSHOT THEIR ASSIGNED ALT.

Narrative

I WAS THE PNF CAPT ON A LEARJET 25 FLT WHICH DEPARTED DENVER; CO; FOR ASPEN; CO. WE HAD BEEN ASSIGNED SEVERAL ALTS DURING THE CLB. WE WERE IN AND OUT OF THE TOPS OF THE CUMULUS CLOUD LAYER WHEN THE DEV OCCURRED AND HAD BEEN ENCOUNTERING LIGHT TO MODERATE TURB. WE WERE ASSIGNED TO CLB TO FL210 BY ZDV AND ADVISED WE HAD TFC AT FL220. AS WE LEVELED AT FL210; THE FO (PF) OVERSHOT SLIGHTLY (100-200 FT). WE MOMENTARILY BROKE OUT OF THE CLOUDS AND SIMULTANEOUSLY OBSERVED AN ACFT WHICH I ESTIMATED TO BE APPROX 1 MI AHEAD OF US. THE FO WAS APPARENTLY SURPRISED AT SIGHTING THE TFC; SAW NO APPARENT MOVEMENT; AND BELIEVED THE TFC WAS CONVERGING ON A COLLISION COURSE. HE INSTINCTIVELY PULLED THE NOSE UP; WHICH TOOK OUR ALT TO FL214 (400 FT ABOVE ASSIGNED ALT). I IMMEDIATELY OBSERVED THE DEV; TOOK OVER THE CTLS; RETARDED PWR; AND PUSHED THE NOSE DOWN. AT THE SAME TIME; ZDV REQUESTED ALT CONFIRMATION. I ADVISED CTR WE HAD OVERSHOT OUR ALT AND WERE CORRECTING. WE EXPEDITIOUSLY RETURNED TO FL210; HOWEVER; THE DEV RESULTED IN A LOSS OF SEPARATION BY ZDV. AT NO TIME DID WE LOSE CTL OF THE ACFT OR DELIBERATELY DEVIATE FROM OUR CLRNC. WE DO NOT BELIEVE THE SAFETY OF EITHER ACFT WAS COMPROMISED. OUR FLT CONTINUED WITHOUT FURTHER INCIDENCE. SUPPLEMENTAL INFO FROM ACN 557477: AS I APCHED FL210; WE WENT FROM IMC TO VMC; AT WHICH TIME I SAW THE BAE146 IN FRONT OF US. I FELT I WAS ON A COLLISION COURSE WITH THE BAE146. THE TIME IT TOOK FOR ME TO RECOGNIZE I WAS NOT ON A COLLISION COURSE WITH THE BAE146 IS THE TIME WE CLBED ABOVE FL210.