Narrative:

While cruising at FL180, I was told to descend to 17000 ft with the altimeter at ord of 30.48. I set 30.48 in my altimeter and noticed that it made a difference of 560 ft. The thought crossed my mind that a VFR at 17500 ft might be at my altitude and I asked ZAU if this was a safe altitude with this high altimeter setting? The response was 'ord altimeter is 30.48.' later, during the flight, I once more asked about the safety of using FL180 with this high altimeter and was told that the ord altimeter was 30.48. Before I left ZAU, I was asked to call ZAU. When I landed at ord, I talked to several pilots and 2 ATC representatives and we all questioned this altitude. I looked at far 91.121 and saw that FL180 was usable with an altimeter of 29.92 or higher. I called a mr X at ZAU and we discussed the problem. He said that they were trying to see if this was an unsafe procedure, but his controller felt that I had been unreasonable on the radio during a busy time on the frequency. Mr X. Said that he would listen to the tape and I said that I had made a reasonable effort to only question during a break and not disturb the controller. Later, I talked to another pilot, and we decided that my reasoning was wrong and I had more separation rather than less as I had first thought. I called ZAU again and tried to contact mr X but was not successful. The person I talked to said he would relay to mr X that I had called again and had figured out there was no safety issue involved. I don't know if the center is going to ask for any action to be taken. Comments: since so many people were confused about the safety involved and I do not carry FARS or the aim on board the aircraft for guidance, I feel that the response from the center was not called for. All the center had to do was say that they would check and everyone would have been satisfied. I think that there might have been controller training in progress as she seemed to be having a hard time and was overctling to a degree. Recommendations: I am going to see if we can include the chart from the FARS in our flight operations manual so that a pilot can quickly find guidance when there is a question about a safe altitude.

Related reports:

Google
 

Original NASA ASRS Text

Title: AN MLG PLT QUESTIONED AN ALT ASSIGNMENT.

Narrative: WHILE CRUISING AT FL180, I WAS TOLD TO DSND TO 17000 FT WITH THE ALTIMETER AT ORD OF 30.48. I SET 30.48 IN MY ALTIMETER AND NOTICED THAT IT MADE A DIFFERENCE OF 560 FT. THE THOUGHT CROSSED MY MIND THAT A VFR AT 17500 FT MIGHT BE AT MY ALT AND I ASKED ZAU IF THIS WAS A SAFE ALT WITH THIS HIGH ALTIMETER SETTING? THE RESPONSE WAS 'ORD ALTIMETER IS 30.48.' LATER, DURING THE FLT, I ONCE MORE ASKED ABOUT THE SAFETY OF USING FL180 WITH THIS HIGH ALTIMETER AND WAS TOLD THAT THE ORD ALTIMETER WAS 30.48. BEFORE I LEFT ZAU, I WAS ASKED TO CALL ZAU. WHEN I LANDED AT ORD, I TALKED TO SEVERAL PLTS AND 2 ATC REPRESENTATIVES AND WE ALL QUESTIONED THIS ALT. I LOOKED AT FAR 91.121 AND SAW THAT FL180 WAS USABLE WITH AN ALTIMETER OF 29.92 OR HIGHER. I CALLED A MR X AT ZAU AND WE DISCUSSED THE PROBLEM. HE SAID THAT THEY WERE TRYING TO SEE IF THIS WAS AN UNSAFE PROC, BUT HIS CTLR FELT THAT I HAD BEEN UNREASONABLE ON THE RADIO DURING A BUSY TIME ON THE FREQ. MR X. SAID THAT HE WOULD LISTEN TO THE TAPE AND I SAID THAT I HAD MADE A REASONABLE EFFORT TO ONLY QUESTION DURING A BREAK AND NOT DISTURB THE CTLR. LATER, I TALKED TO ANOTHER PLT, AND WE DECIDED THAT MY REASONING WAS WRONG AND I HAD MORE SEPARATION RATHER THAN LESS AS I HAD FIRST THOUGHT. I CALLED ZAU AGAIN AND TRIED TO CONTACT MR X BUT WAS NOT SUCCESSFUL. THE PERSON I TALKED TO SAID HE WOULD RELAY TO MR X THAT I HAD CALLED AGAIN AND HAD FIGURED OUT THERE WAS NO SAFETY ISSUE INVOLVED. I DON'T KNOW IF THE CTR IS GOING TO ASK FOR ANY ACTION TO BE TAKEN. COMMENTS: SINCE SO MANY PEOPLE WERE CONFUSED ABOUT THE SAFETY INVOLVED AND I DO NOT CARRY FARS OR THE AIM ON BOARD THE ACFT FOR GUIDANCE, I FEEL THAT THE RESPONSE FROM THE CTR WAS NOT CALLED FOR. ALL THE CTR HAD TO DO WAS SAY THAT THEY WOULD CHK AND EVERYONE WOULD HAVE BEEN SATISFIED. I THINK THAT THERE MIGHT HAVE BEEN CTLR TRAINING IN PROGRESS AS SHE SEEMED TO BE HAVING A HARD TIME AND WAS OVERCTLING TO A DEG. RECOMMENDATIONS: I AM GOING TO SEE IF WE CAN INCLUDE THE CHART FROM THE FARS IN OUR FLT OPS MANUAL SO THAT A PLT CAN QUICKLY FIND GUIDANCE WHEN THERE IS A QUESTION ABOUT A SAFE ALT.

Data retrieved from NASA's ASRS site as of July 2007 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.