Figure 2-68. ATC reporting procedures.  settings in hectopascals (hPa) (millibars). Therefore, it is  imperative that pilots or on-board equipment are able  to accurately convert inches of mercury to hPa, or hPa to  inches of mercury.  A local altimeter setting equivalent to the barometric  pressure measured at an airport altimeter datum, usually  signifying the approach end of the runway is in use. At the  airport altimeter datum, an altimeter set to QFE indicates  zero altitude. If required to use QFE altimetry, altimeters  are set to QFE while operating at or below the transition  altitude and below the transition level. On the airport, the  altimeter will read “0” feet.  Use the altimeter setting (en route) at or above the  transition altitude (FL 180 in the United States). The  altimeter setting is always 29.92 inches of mercury/1013.2  hPa for a QNE altitude. Transition levels differ from country  to country and pilots should be particularly alert when  making a climb or descent in a foreign area.  A local altimeter setting equivalent to the barometric  pressure measured at an airport altimeter datum and  corrected to sea level pressure. At the airport altimeter  datum, an altimeter set to QNH indicates airport elevation  above mean sea level (MSL). Altimeters are set to QNH  while operating at and below the transition altitude and  below the transition level.  For flights in the vicinity of airports, express the vertical  position of aircraft in terms of QNH or QFE at or below the  transition altitude and in terms of QNE at or above the  transition level. While passing through the transition layer,  express vertical position in terms of FLs when ascending  and in terms of altitudes when descending.  When an aircraft that receives a clearance as number one  to land completes its approach using QFE, express the  vertical position of the aircraft in terms of height above  the airport elevation during that portion of its flight for  which you may use QFE.  It is important to remember that most pressure altimeters  are subject to mechanical, elastic, temperature, and  installation errors. In addition, extremely cold temperature  differences may also require altimeter correction factors  as appropriate.  2-45  Barometric Pressure for Local Altimeter Setting  (QNH)  Barometric Pressure for Standard Altimeter  Setting (QNE)  Altitude Above Ground (QFE)  RADAR/NON-RADAR REPORTS  These reports should be made at all times without a specific ATC request.  Leaving one assigned flight altitude or flight level for another  VFR-on-top change in altitude  Leaving any assigned holding fix or point  Missed approach  Unable to climb or descend at least 500 fpm  TAS variation from filed speed of 5% or 10 knots, whichever  is greater  Time and altitude or flight level upon reaching a holding fix  or clearance limit  Loss of Nav/Comm capability (required by Part 91.187)  Unforecast weather conditions or other information relating  to the safety of flight (required by Part 91.183)  "Marathon 564, leaving 8,000, climb to 10,000."  "Marathon 564, VFR-on-top, climbing to 10,500."  "Marathon 564, leaving FARGO Intersection."  "Marathon 564, missed approach, request clearance to Chicago."  "Marathon 564, maximum climb rate 400 feet per minute."  "Marathon 564, advises TAS decrease to140 knots."  "Marathon 564, FARGO Intersection at 05, 10,000, holding east."  "Marathon 564, ILS receiver inoperative."  "Marathon 564, experiencing moderate turbulence at 10,000."  NON-RADAR REPORTS  When you are not in radar contact, these reports should be made without a specific request from ATC.  Leaving FAF or OM inbound on final approach  Revised ETA of more than three minutes  "Marathon 564, outer marker inbound, leaving 2,000."  "Marathon 564, revising SCURRY estimate to 55."  REPORTS  EXAMPLE  REPORTS  EXAMPLE 