August 12, 20223 yr The ICAO definition of transition altitude (per ICAO Annex 15) is: "The altitude at or below which the vertical position of an aircraft is controlled by reference to altitudes." So flight at the transition altitude under ICAO rules should be done with QNH set. The US FAA AIP says that the altimeter should be set to QNE (29.92in/1013HPa) at or above 18,000 ft (AIP para 3.3.2), so flight at the US standard transition altitude (FL180) is done with QNE set. The key is in how the altitude is specified by ATC. US ATC will never clear you to "18,000 ft", but only to FL180. If an EU controller clears you to "FL50" that signifies a flight level at QNE...if they clear you to 5,000 ft, that means an altitude with QNH set. Similarly, restrictions in published procedures will be specified as a QNH-based altitude (e.g. at/above 5000 is depicted as 5000) or as a QNE-based flight level (e.g. at/above FL50 is depicted as FL50). When in doubt, as always, query the controller. Bob Scott | President and CEO, AVSIM Inc ATP Gulfstream II-III-IV-V Sys1 (MSFS20+24/XPlane12+11): AMD 9800X3D, water 2x240mm, MSI MPG X670E Carbon, 64GB GSkill 6000/30, nVidia RTX4090FE Alienware AW3821DW 38" 21:9 GSync, 2x4TB Crucial T705 PCIe5 + 2x2TB Samsung 990 SSD, EVGA 1000P2 PSU, 12.9" iPad Pro Thrustmaster TCA Boeing Yoke, TCA Airbus Sidestick, Twin TCA Airbus Throttle quads, PFC Cirrus Pedals, Coolermaster HAF932 case Sys2 (P3Dv5/v4): i9-13900KS, water 2x360mm, ASUS Z790 Hero, 32GB GSkill 7800MHz CAS36, ASUS RTX4090 Samsung 55" JS8500 4K TV@60Hz, 3x 2TB WD SN850X 1x 4TB Crucial P3 M.2 NVME SSD, EVGA 1600T2 PSU Fiber link to Yamaha RX-V467 Home Theater Receiver, Polk/Klipsch 6" bookshelf speakers, Polk 12" subwoofer, 12.9" iPad Pro PFC yoke/throttle quad/pedals with custom Hall sensor retrofit, Thermaltake View 71 case, Stream Deck XL button box Sys3 (DCS/P3Dv4/ATS/ETS): AMD 7800X3D, MSI MPG X870E Carbon, Noctua NH-D15S, 64GB GSkill 6000/30, EVGA RTX3090 Alienware AW3420DW 34" 21:9 GSync, Corsair HX1000i PSU, 4TB Crucial T705 PCIe5 + 2TB Samsung 970Evo Plus, TM TCA Officer Pack, Saitek combat pedals, TM Warthog, TM RS300 FF wheel/pedals, Coolermaster HAF XB case
August 13, 20223 yr Been a long time since I flew commercially, but when I did (small turboprops) the company procedure was climbing, once cleared to a flight level the pilot flying would set standard straight away, no matter what altitude he was at, and in descent, once cleared to an altitude, the pilot flying would set the QNH straight away. The logic being, if the pilot flying waited until the transition altitude, sooner or later he'll miss the exact moment, and could cause a loss of separation, in descent, even more important, very low barometric pressure could have the aircraft a thousand feet lower than the equivalent flight level, with terrain separation implications. Eugene
October 16, 20223 yr Moderator Sorry for the late post. As a long time user and supporter of Radar Contact we often had complaints about the program telling the user they weren’t at the correct altitude / flight level. It’s a very simple rule. If you’re instructed to climb / descend to an altitude you should be on QNH. If instructed to climb / descend to a flight level you should be on Std Pressure. So to answer @sunnydaze’s question you would remain on QNH until cleared higher. I live right under the LISTO departure from 05. 😁 Ray (Cheshire, England). System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke, Fulcrum Throttle Quadrant. Cheadle Hulme Weather website.
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