Date: 201702
Local time of day: 1201-1800
Location: ZAU.ARTCC, IL
Light: Daylight
Aircraft: Light Transport; Low Wing; 2 Turbojet Eng
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E ZAU
ATC / advisory: Center ZAU
Aircraft component: Altimeter
Component problem: Improperly Operated
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Distraction; Human-Machine Interface; Situational Awareness
Second reporter function: Pilot Flying; Single Pilot
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Equipment / Tooling; Human Factors
Primary problem: Equipment / Tooling

Narrative: Aircraft X checked on descending to 14000; and was issued the MSN altimeter. Soon thereafter MKE approach called up and said point out approved on Aircraft X. At this time we noticed that Aircraft X was at 13100 instead of his assigned 14000. We queried the pilot as to his altitude and he replied that he was level 140. We informed him that we showed him at 13100 and he said was descending to 13000 and requesting lower. We told him to maintain 13000 and that we'd have lower for him in a couple of miles. We then noticed that his altitude was varying between 12000 and 13000. When we issued 11000 and to switch to MSN approach; we received no response for several minutes and several attempts by us and MSN approach both. When he finally checked back on; we shipped Aircraft X to MSN approach. Upon further investigation and a call back from the pilot; it was discovered that the pilot had initially input the altimeter incorrectly as 30.43 instead of 29.43 causing his altitude to be 1000 feet off. Then the pilot tried to switch over to get the MSN ATIS and we lost communications until he came back over.


Second narrative: While on a return FAR Part 91 flight Madison; WI (MSN) while working with Chicago ARTCC and descending through FL260; I had received a 'descend and maintain' clearance to '14;000 feet'. Earlier; somewhere just east of Lake Michigan; I listened to the (MSN) Automated Terminal Information Service (ATIS) briefing three times; as a result of being distracted by the routine ATC communications; check-ins; clearances and the ATIS interruptions due to the not uncommon frequency crossover from other nearby ATC facilities. As I normally do; I dialed the altimeter setting in the standby altimeter as a reminder for when transitioning from pressure to indicated altitudes. Passing just below FL180 I set both primary altimeters to 30.44' referencing the standby altimeter setting. The autopilot leveled the airplane at 14;000. Within approximately one minute of my level-off; the controller asked 'Aircraft X say altitude'; which after quickly verifying; I replied '14;000 feet'. Almost immediately after that; the controller stated that he showed me at 13;000 feet. Assuming the controller's information was correct; I asked for amended clearance to 13;000 and was eventually given it. I switched back to the MSN ATIS on the number two communications radio to check the local altimeter setting and distinctly heard 29.44 inches which would have cause the discrepancy.While there is no excuse for my mistake; I believe there are extenuating circumstances that may have contributed to my incorrectly setting the altimeters. 1. It had been a fairly long day with an early show time at the airport which was probably a factor. 2. While setting or verifying my transition altimeter setting; I was fighting a bright sun over a reflective lower cloud deck which made it more difficult to see the small LED digital display of the standby altimeter. I had effectively blocked the sun while sitting upright; however when leaning forward to adjust the standby altimeter I had the full effect of the sunlight. 3. The sunglasses that I was wearing; were not very compatible with the small colored display of the digital standby unit and in retrospect; combined with the suns glare; may have caused me to think I dialed the correct setting when in fact it was off 1 inch Hg after listening to the ATIS.When transitioning through FL180; especially on descent; I should have re-verified with ATC; ATIS or the onboard aircraft weather information the latest barometric altimeter setting as opposed to relying on one source of information.


Synopsis: ZAU Controller and pilot reported the aircraft was at the wrong altitude due to an incorrect altimeter setting.