Highest QNH

[Ultralights]

looking at the weather chart today, the High pressure system over Tassie is now at 1043 hp, thats the highest i can ever recall.

 

whats the highest QNH setting ever used? or can be used?

 

 

[facthunter]

Dunno.QNH?

 

I'll bite. WHEN WOULD'NT you use the actual figure. It would be meaningless otherwise. The Alt has to read aerodrome height relative to MSL. There is a tolerance allowed in the instrument, outside of which it's unserviceable. IF the QNH is not accurately set all your approaches (instrument) and circuit heights are SUSS. Nev

 

 

[pilotdave69]

hey,

 

Over last 2 days we have had 1034 and 1035 in Bathurst NSW, highest i ever remember seeing it, made for nice flying over last 2 days, especially circuits. 1043 is very high though.

 

Dave

 

 

[Bruce Robbins]

I believe most altimeters only go up to 1050 mb.

 

A quick internet search turned this up, from the FAA. Didn't check whether it is still current.

 

Sec. 91.144 Temporary Restriction on Flight Operations During Abnormally High

 

Barometric Pressure Conditions.

 

 

 

(a) Special flight restrictions. When any information indicates that

 

barometric pressure on the route of flight currently exceeds or will exceed

 

31 inches of mercury, no person may operate an aircraft or initiate a flight

 

contrary to the requirements established by the Administrator and published

 

in a Notice to Airmen issued under this section.

 

(b) Waivers. The Administrator is authorized to waive any restriction

 

issued under paragraph (a) of this section to permit emergency supply,

 

transport, or medical services to be delivered to isolated communities, where

 

the operation can be conducted with an acceptable level of safety.

 

 

 

 

 

Federal Register Notes

 

 

 

59 FR 17450, No. 70, Apr. 12, 1994

 

 

 

SUMMARY: This final rule amends part 91 of the Federal Aviation Regulations

 

(FAR) to provide for the issuance of temporary flight restrictions on certain

 

operations when accurate altitude information is not available. The rule is

 

warranted because barometric pressure higher than 31.00 inches of mercury

 

(inHg) (1049.8 millibars) exceeds the capability of standard aircraft

 

pressure altimeters and prevents the display of accurate altitude

 

information. The rule provides restrictions on certain flight operations

 

during periods of abnormal atmospheric pressure conditions and is necessary

 

to promote flight safety during certain operations for which accurate

 

altitude information is critical.

 

 

 

EFFECTIVE DATE: May 12, 1994.

 

 

[Ultralights]

yep NEv, agree with you, but i miss worded the question, what i meant to say is, is there a upper limit to the QNH subscale setting? and basically if anyone has ever had to use a setting that high!

 

 

[HEON]

Thats nice to know. Jumped into a aircraft today and dialed in the airfield altitude...thought I had letter get the altimeter tested as the reading was so high! Seems no need.

 

 

[Guest Howard Hughes]

I don't know about highs, but once saw a low over the Bight of 943, tried to wind the subscale down, and that low was too low!:ah_oh:

 

 

[Ultralights]

with a high of 1043 there has to be a very deep low somewhere nearby! wonder whats happening in Antarctica with there band of antarctic Lows?

 

just checked, 955 mb, with winds of 110 Kts!

 

 

[facthunter]

Where you are.

 

U/L you are right in suggesting that things are not normal. You are in effect 900' below where you normally are Baro wise. the aeroplane would perform very well. nev