inches or hPa
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The sooner the entire world goes to full metric the better.
What about RVR in metres and cloudbase in feet? Or wind in metres per second?
At least the USA is consistently imperial (apart from temperature).
By the way whose statutes define one mile - US or UK?
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Pontius 
Just trying to simplify that decision making flow chart for those who work for big British airlines. When across the pond, you may remove all the boxes, arrows, and diamonds representing the extra steps for figuring out which instrument(s) should be adjusted in response to QNH information. 
And, oh my god, I've just thought of another thing that will probably cause me to crash and it's certainly worth investigating immediatley; the Yanks say 'altimeter setting' and not 'QNH' 
Just think what problems THAT could cause........(none for me but, no doubt, a worthless HF exercise would say otherwise).
Just think what problems THAT could cause........(none for me but, no doubt, a worthless HF exercise would say otherwise).
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I would suggest that going "full metric" is about the biggest change in the arena of aviation that could possibly be contemplated.
There must be many, many more aircraft equipped with altimeters in feet and ASIs in knots than there are using metres and km/h. Consequently, the vast majority of the world's pilots and air traffic controllers are trained in such units. Moreover, the more complex Air Traffic management systems such as that found NAT region are built around western aviation units. I shudder to think what it would cost to recalibrate all these aircraft, computers, pilots and controllers to operate in metres.
The argument about standardizing the altimeter subscale setting is tiny in comparison to this can of worms.
There must be many, many more aircraft equipped with altimeters in feet and ASIs in knots than there are using metres and km/h. Consequently, the vast majority of the world's pilots and air traffic controllers are trained in such units. Moreover, the more complex Air Traffic management systems such as that found NAT region are built around western aviation units. I shudder to think what it would cost to recalibrate all these aircraft, computers, pilots and controllers to operate in metres.
The argument about standardizing the altimeter subscale setting is tiny in comparison to this can of worms.
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Really?
"Let us consider the United States of America.
In the USA, there are located thousands more aircraft than the rest of the world, combined.
I'm not just talking airliners, I'm considering all aircraft, airline, general aviation and military.
Here, we use inches of mercury for setting the pressure altimeter.
Always have, always will."
Really? The links I searched to back up your statement about aircraft numbers were inconclusive, but none indicated there were thousands more in the US than the rest of the world combined. "Always have, *always will* ??" So certain about the future? Next time I go to the racetrack, or sit at a roullette wheel, can I take you with me?
In the USA, there are located thousands more aircraft than the rest of the world, combined.
I'm not just talking airliners, I'm considering all aircraft, airline, general aviation and military.
Here, we use inches of mercury for setting the pressure altimeter.
Always have, always will."
Really? The links I searched to back up your statement about aircraft numbers were inconclusive, but none indicated there were thousands more in the US than the rest of the world combined. "Always have, *always will* ??" So certain about the future? Next time I go to the racetrack, or sit at a roullette wheel, can I take you with me?
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Of course our neighbours to the south aren’t the only ones that use inches of mercury. There is that country north of the 49th parallel that will normally provide an altimeter setting in inches and landing minima in feet and miles (or fractions thereof). After I land though, I drive x kilometers to home/hotel at a posted speed of x kilometers per hour while listening to the radio in the car giving me the weather in degrees Celsius and the atmospheric pressure in hPa.
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The US always have and always will use inches Hg.
Just like the US army always have and always will use miles and yards.
Just like the US scientific community always have and always will refuse to go SI, no matter how many kinetic Mars probes they send off.
Just like the US army always have and always will use miles and yards.
Just like the US scientific community always have and always will refuse to go SI, no matter how many kinetic Mars probes they send off.
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Slightly off topic but...
For dman59 - although it's a bit off topic, you perhaps didn't try very hard to find the aircraft statistics. For rule of thumb use, there are about 250,000 active aircraft in the USA, there are about 50,000 active aircraft in Europe, and there are surprisingly few (a few thousand here and there, with Canada and Australia/NZ as reasonable fleets) in the whole of the rest of the world put together.
So, there is a reason why the US might feel a level of tail-wags-dog if you think they are going to change things to match the rest of the world.
So, there is a reason why the US might feel a level of tail-wags-dog if you think they are going to change things to match the rest of the world.
ATC : "Descend to altitude 5,000 feet, on QNH 1009 hPa."
US Pilot: "Can I have that in inches, please."
ATC : "Certainly - Descend to 60,000 inches on QNH 1009 hPa."
US Pilot: "Can I have that in inches, please."
ATC : "Certainly - Descend to 60,000 inches on QNH 1009 hPa."
Pontius, Re #19, you appear to look at this problem from just a single viewpoint, which strengthens an old-style view of human error; i.e. it’s always pilot error. Whereas with a wider view, a systems (operational) approach might enable a better balance of possible contributing factors.
To maintain the required level of safety, as I hope that you would agree, it is necessary to consider the combination of the human element and components of the operational situation.
You are correct in expecting pilots to use their brains – to think, prepare, and avoid expectation bias, but even the best (and those who think they are) will suffer error.
Error is the result, not the intent of an operation. Often it is the human weakness, the limits of our performance, which contribute to error. If such conditions occur in combination with operational situations which also provide opportunity for error, then the safety risks will increase. These situations could include all crew members being tired, failing to recall previous briefings, experiencing high workload due to thinking about other issues, or being distracted.
A small but perhaps significant contribution to reducing the safety risks in a situation involving hPa or in, might be achieved by using a world standard; this is the intent of the ICAO agreement, and if implemented might also mitigate an error or poor practice by ATC etc, as well as those from our frail ‘self’.
There is increasing emphasis on trapping errors, but if the trap includes human activity what then are the protections from the consequences of poor human performance. We depend on defences in-depth, not only people, but also systems, procedures, and processes, which have to be repeated continuously; yet even all of these are not totally error proof, but if failure is sufficiently rare, then the resultant risks are tolerated.
I ‘trapped’ my error when breaking cloud over the sea; “where are we – how goes it”, something looked wrong, and it took some time to establish the cause. Now if the situation had involved being overland, lower cloud, or I had less time, then the outcome might not be so easily shared.
Sharing experiences might not change national procedure, but provide opportunity for individual learning where that knowledge might just be recalled in similar circumstances.
What if you are flying a transatlantic diversion into KEF due to failure / emergency, the weather is poor, it been a long series of sectors, then the same opportunities for error might exist. A good diversion checklist would supplement background training and personal knowledge … , but would the same checks and knowledge apply to a diversion into Sondrestrom or Iqualuit?
To maintain the required level of safety, as I hope that you would agree, it is necessary to consider the combination of the human element and components of the operational situation.
You are correct in expecting pilots to use their brains – to think, prepare, and avoid expectation bias, but even the best (and those who think they are) will suffer error.
Error is the result, not the intent of an operation. Often it is the human weakness, the limits of our performance, which contribute to error. If such conditions occur in combination with operational situations which also provide opportunity for error, then the safety risks will increase. These situations could include all crew members being tired, failing to recall previous briefings, experiencing high workload due to thinking about other issues, or being distracted.
A small but perhaps significant contribution to reducing the safety risks in a situation involving hPa or in, might be achieved by using a world standard; this is the intent of the ICAO agreement, and if implemented might also mitigate an error or poor practice by ATC etc, as well as those from our frail ‘self’.
There is increasing emphasis on trapping errors, but if the trap includes human activity what then are the protections from the consequences of poor human performance. We depend on defences in-depth, not only people, but also systems, procedures, and processes, which have to be repeated continuously; yet even all of these are not totally error proof, but if failure is sufficiently rare, then the resultant risks are tolerated.
I ‘trapped’ my error when breaking cloud over the sea; “where are we – how goes it”, something looked wrong, and it took some time to establish the cause. Now if the situation had involved being overland, lower cloud, or I had less time, then the outcome might not be so easily shared.
Sharing experiences might not change national procedure, but provide opportunity for individual learning where that knowledge might just be recalled in similar circumstances.
What if you are flying a transatlantic diversion into KEF due to failure / emergency, the weather is poor, it been a long series of sectors, then the same opportunities for error might exist. A good diversion checklist would supplement background training and personal knowledge … , but would the same checks and knowledge apply to a diversion into Sondrestrom or Iqualuit?
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The number of mistakes resulting from differing units pale into insignificance compared to the number of mistakes that would result from changing units. If you were to change over to hPa in the US, you'd be scraping people of hillsides for decades to come. Ditto if introducing inHg in Europe.
Those pilots who actually fly from an area where inHg is used into an area where they use hPa would typically be long-haul airliner crews... One would hope that those crews are of sufficient standard that accidents would rarely result from such mistakes. As safetypee illustrates; he successfully trapped his error and the outcome was good.
Those pilots who actually fly from an area where inHg is used into an area where they use hPa would typically be long-haul airliner crews... One would hope that those crews are of sufficient standard that accidents would rarely result from such mistakes. As safetypee illustrates; he successfully trapped his error and the outcome was good.
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hPa and Inches
Old standardization problem...
I was with PanAm from 1969 until 1991... Many years on furlough.
Inches, or hPa never bothered us. PanAm was essentially international operator.
We always specified "inches" or "hPa" in our check-lists and SOPs.
With the merge of National Airlines 1979, we got a lot of "domestic crews"...
Even on US domestic sectors, we spoke "QNH" or "QNE" settings.
Our colleagues with TWA and NW, or BNF never had any problems, either.
xxx
TWA as an example, had a 1 week/40 hrs classroom for "international operations" training.
All US supplemental carriers, i.e. World, TIA-Transamerica, ONA (and others) had same or equivalent.
I recall PanAm assisted UAL for "international training" of their crews.
xxx
Now you all say "metric" - even the Russians and China had to learn hPa.
In the old days they did not use hPa. Their units, originally were "mm of Mercury".
760 millimeters of Hg was STD = 29.92 or 1013.2...
I remember an old AN-2 that had a metric altimeter with mm.Hg...
And back then, we called hPA to be mB - milliBars...
xxx
Little by little, USA will go to ICAO units...
Eventually, they will use hPa... will take time, many more years maybe.
After all, they changed their ATIS and temperatures to ºCelsius.
Eventually, will be meters and kilometers for visibilities.
And liters or kilos for volumes and weights, like Canada did...
Still a lot of "Rednecks" working for the FAA... but eventually they will retire.
Like me... I retire in 2 months, and happy I will forget all about planes.
xxx
Keep on fighting for "metric" or not... makes me laugh.
Happy contrails
I was with PanAm from 1969 until 1991... Many years on furlough.
Inches, or hPa never bothered us. PanAm was essentially international operator.
We always specified "inches" or "hPa" in our check-lists and SOPs.
With the merge of National Airlines 1979, we got a lot of "domestic crews"...
Even on US domestic sectors, we spoke "QNH" or "QNE" settings.
Our colleagues with TWA and NW, or BNF never had any problems, either.
xxx
TWA as an example, had a 1 week/40 hrs classroom for "international operations" training.
All US supplemental carriers, i.e. World, TIA-Transamerica, ONA (and others) had same or equivalent.
I recall PanAm assisted UAL for "international training" of their crews.
xxx
Now you all say "metric" - even the Russians and China had to learn hPa.
In the old days they did not use hPa. Their units, originally were "mm of Mercury".
760 millimeters of Hg was STD = 29.92 or 1013.2...
I remember an old AN-2 that had a metric altimeter with mm.Hg...
And back then, we called hPA to be mB - milliBars...
xxx
Little by little, USA will go to ICAO units...
Eventually, they will use hPa... will take time, many more years maybe.
After all, they changed their ATIS and temperatures to ºCelsius.
Eventually, will be meters and kilometers for visibilities.
And liters or kilos for volumes and weights, like Canada did...
Still a lot of "Rednecks" working for the FAA... but eventually they will retire.
Like me... I retire in 2 months, and happy I will forget all about planes.
xxx
Keep on fighting for "metric" or not... makes me laugh.
Happy contrails
