Setting Kohlsman to allow agl indication?

[Let'sgoflying!]

This is a 1995 incident.
In it, they discuss setting the altimeters to a ‘made up’ alt setting which would cause the altimeters to read AGL, ie 0’agl upon touchdown.

Is this practice still going on in commercial US aviation?
I remember reading the military flight demonstration teams doing this, and some foreign airlines but never domestic carriers.
Any other info on the practice?
Has the FAA waded in, sometime in the past?


7:38

 

[farmrjohn]

It's QFE: https://en.wikipedia.org/wiki/Altimeter_setting

 

[Rgbeard]

It's QFE: https://en.wikipedia.org/wiki/Altimeter_setting

Sorry. QFE?

 

[MauleSkinner]

Sorry. QFE?

1. QFE is the barometric altimeter setting that causes an altimeter to read zero when at the reference datum of a particular airfield (in practice, the reference datum is either an airfield center or a runway threshold). In ISA temperature conditions the altimeter will read height above the airfield/runway threshold in the vicinity of the airfield.

 

[sourdough44]

I think Russia was doing it not long ago, maybe still are? When used to the other way, seems a little bass-ackwards. I think the whole world should go to Standard above 180. No I don’t want to discuss the differences with 180 whether a low or high local altimeter setting.


Just use 180 everywhere, easy.

 

[midlifeflyer]

1. QFE is the barometric altimeter setting that causes an altimeter to read zero when at the reference datum of a particular airfield (in practice, the reference datum is either an airfield center or a runway threshold). In ISA temperature conditions the altimeter will read height above the airfield/runway threshold in the vicinity of the airfield.

...and it's used in some countries. Dual altimeters even. One QFE and one QNH. I remember that from the time I flew in the UK.

 

[Rgbeard]

...and it's used in some countries. Dual altimeters even. One QFE and one QNH. I remember that from the time I flew in the UK.

sorry. I am a dumb ass American and this is foreign to me. (Posted from rural Mexico)

 

[Albany Tom]

Sounds like a weird idea to me. I guess it could work in the flat states? Not exceptionally well here. And sounds like a pretty lousy idea out west..

I mean, if you don't know how high the hills are around you, and the elevation of the airport you're landing at, maybe flying isn't your thing.

 

[Busflyer]

American did it for years. They got away from that procedure after the MD-88 accident at BDL.

 

[Tusayan]

The UK is probably the worst, they’ll have a single controller working planes on three different altimeter settings depending on altitude and preference (QFE, QNH and standard/1013 hPa above some very low transition altitude). CTAF is unknown and they also have something called a regional setting, which most people ignore. Planes announce which altimeter setting they’re using when making contact, ATC has to sort out separation and some people there cannot understand how it could be any other way. It’s a complete CF.

 

[Pinecone]

Gliders do it all the time.

Set altimeter to read 0 before take off.

 

[Let'sgoflying!]

American did it for years. They got away from that procedure after the MD-88 accident at BDL.

That's the one. In the video.

Is this practice still going on in commercial US aviation?

Has the FAA waded in, sometime in the past?

 

[Albany Tom]

The UK is probably the worst, they’ll have a single controller working planes on three different altimeter settings depending on altitude and preference (QFE, QNH and standard/1013 hPa above some very low transition altitude). CTAF is unknown and they also have something called a regional setting, which most people ignore. Planes announce which altimeter setting they’re using when making contact, ATC has to sort out separation and some people there cannot understand how it could be any other way. It’s a complete CF.

Reminds me of a story. A guy is riding in a car with a co-worker for the first time. They're cruising along around 60 mph, and come up on a red light. Driver doesn't even slow down. The passenger says "you know that's a red light, right?" Driver says "yep!" and proceeds to drive straight through it, full speed. Passenger cringes, yells "what the hell are you doing?" Driver replies "calm down. My brother Ed drives like this all the time. Never had an accident." Passenger promises himself to never ride with this nut again, as the driver blows through 2 more lights. Just as he's getting used to that, he sees a light change from red to green. Driver slams on the brakes, car slides to a stop just before the light. Passenger yells "Now what the f87k are you doing??" Driver looks back as if the passenger is nuts, and says "Ed might be going across."

 

[Shuckers86]

I think I remember when jumpseating on American back in the 90s they used QFE.

 

[Busflyer]

No one in the US uses it anymore as far as I know.

 

[Dana]

Flying NORDO putt-putts on local flights over the flatlands of NJ in the 1980s, it was pretty common to set the altimeter to zero on the ground.

 

[WDD]

I understand that people used to do that. I fly from a towered airport in busy airspace and flies IFR for anything nom local - I can’t get my head in that space FWIW.

 

[Larry in TN]

QNH is setting your local altimeter setting and what most GA airplanes do all of the time.
QNE is setting 29.92 which we do when above the transition altitude (18,000/FL180 in the US).
QFE is setting an altimeter setting so that the altimeter displays height above field elevation.

Memory aid:
QNH - NH = Near Home
QNE - NE = Nearly Everywhere
QFE - FE - Field Elevation

QFE is still used in some places in the world, but not many. AAL used QFE for decades. The newer airplanes with integrated flight management systems don't do QFE as easily as the older tech (pre-757/767/A320) airplanes did.

AAL's old procedure was to set QNH on the standby altimeter and QFE on the pilot's primary altimeters.

The real problems with the BDL accident were continuing in that weather and using the wrong autopilot modes which allows the undershoot of the MDA level-off.

 

[Deelee]

I think the whole world should go to Standard above 180

I agree. As a 'murcan I find it odd that some countries have transition altitudes of 5000', 6000', etc... or sometimes transition alt is given by ATC (wTf?). So you end up with flight levels of FL80, FL100 .... bizzare.

18,000' everywhere! Murca!

Dual altimeters even. One QFE and one QNH

I think various Airbi have a knob that lets you switch between QFA/QNH. Inner knob under the altimeter setting knob. Strange and fascinating machines, those Airbi.

 

[WDD]

I just assumed that it was all standardized internationally. Since I’m unlikely to fly a Skyhawk across the Atlantic or even across the border I’m good. I’m again amazed on what I learn here.

 

[RussR]

AAL's old procedure was to set QNH on the standby altimeter and QFE on the pilot's primary altimeters.

That seems so bizarre. Obviously it was SOP and must have worked okay, but how does that work?

Field elevation is 1072. ATC says "climb and maintain 8000". So what do you do, put 6928 in the autopilot altitude selector?

 

[Greg Bockelman]

I don’t think they did it for departures, only below a certain altitude on arrival.

 

[Larry in TN]

I agree. As a 'murcan I find it odd that some countries have transition altitudes of 5000', 6000', etc... or sometimes transition alt is given by ATC (wTf?). So you end up with flight levels of FL80, FL100 .... bizzare.

It adds to the workload.

Aruba, is a good one. It has a transition altitude of 2,500' (climbing) and a transition level (descending) of FL040.

Mexico is 18,500'/FL195. Guess they just wanted to be different? I don't know.

That seems so bizarre. Obviously it was SOP and must have worked okay, but how does that work?

Field elevation is 1072. ATC says "climb and maintain 8000". So what do you do, put 6928 in the autopilot altitude selector?

I never figured that out. I rode in their jumpseats when they were using QFE procedures but never figured out the details.

 

[Larry in TN]

I don’t think they did it for departures, only below a certain altitude on arrival.

My recollection was it was both departure and arrival but that was a long time ago (early to mid 1990s).

 

[Greg Bockelman]

I could be wrong, but I don’t see the point of doing it on departure.

 

[Deelee]

only below a certain altitude on arrival.

Was this before we had radar altimeters? It would (sort of) make sense in that case.

 

[RussR]

I don’t think they did it for departures, only below a certain altitude on arrival.

Okay, but it's still the same question for a descent. They give you "Descend and maintain 3000", how did that work re: autopilot altitude preselect, and what displayed altitude you level off at? You'd be seeing (in my scenario) 928 ft on the altimeter.

Or was it only set to QFE once you were on final approach?

 

[Greg Bockelman]

Honestly I don’t recall. I had only jumpseated on American a few times before they changed the procedure. Logically, it makes sense to change to Qfe when cleared for the approach, but I just don’t remember.

 

[Greg Bockelman]

Was this before we had radar altimeters? It would (sort of) make sense in that case.

We’ve had radar altimeters for a long time. Their procedure was in place long after radar altimeters were in use.

 

[Cap'n Jack]

I could be wrong, but I don’t see the point of doing it on departure.

The only reason I could guess is if you had to return to the airport for some reason. Sort of like departing IFR with some minimum visibility in case I need to return.

 

[Doug Reid]

If you fly in an airshow, setting the altimeter to read agl is often the norm.

 

[WDD]

If you fly in an airshow, setting the altimeter to read agl is often the norm.

Makes sense as there will be no other traffic you might run into - just the ground.

 

[brcase]

Gliders do it all the time.

Set altimeter to read 0 before take off.

It did used to be common in the US for Gliders to do this. Especially at training facilities where all they were doing pretty much doing up and down flights. I think most places have gotten away from it. But I am sure some, maybe more than I realize, are still doing it.

Once we start flying cross country flights it no longer makes sense to do so. A number western locations it is not possible to set the Altimeters to Zero. This week I am flying at of an airport at 6000ft msl.

Brian
CFIIIG/ASEL
LS6b N1720

 

[Ed Haywood]

I set to zero before takeoff for aerobatic practice and contests. Mental math to calculate AGL while pulling G's is asking for trouble.

Thunderbirds learned this the hard way:

"There is clear and convincing evidence that pilot error caused the mishap," the report added. "The pilot misinterpreted his altitude above the ground causing him to roll and apex approximately 1,000 feet below the target altitudes. He mistakenly interpreted 4,500 feet MSL as the planned 2,500 feet AGL roll altitude and 5,500 feet MSL as the target 3,500 foot AGL apex altitude. Thus, upon reading 5,500 feet MSL on the altimeter, he called "three five" and initiated a Split S that the aircraft was incapable of successfully completing prior to ground impact."

Three factors, the report said, "substantially contributed to creating the prospect for such a critical error.

"The requirement for demonstration pilots to real time convert MSL to AGL numbers, a maneuver with a limited margin of error, and a preconscious level of awareness created a situation more susceptible to pilot error."​

 

[Larry in TN]

I could be wrong, but I don’t see the point of doing it on departure.

I guess it makes your cleanup schedule easier, back before VNAV handled that for us. Same for the engine-out acceleration altitude.

Was this before we had radar altimeters? It would (sort of) make sense in that case.

No, radar altitudes have been in transport aircraft for a very long time. They were used for CATII and CATIII approaches as a primary input for the ground proximity systems (GPWS).

 

[3393RP]

Gliders do it all the time.

Set altimeter to read 0 before take off.

I always did so before takeoff in a hang glider. Knowing how high you had thermaled above the launch altitude was good for bragging rights and some beers at the post flight landing area.

 

[Hang 4]

I always did so before takeoff in a hang glider. Knowing how high you had thermaled above the launch altitude was good for bragging rights and some beers at the post flight landing area.

I used to do the same launching from a mountain. Might be 20 min or more before it turned into a positive number.

 

[JoeInCT]

Has to make things a bit tougher when ATC calls out traffic. Especially if they are closing and are +/- a few hundred feet. No thanks.

 

[jrcox19]

Has to make things a bit tougher when ATC calls out traffic. Especially if they are closing and are +/- a few hundred feet. No thanks.

If you're in the same area, you're also using the same QFE, so... no difference?

 

[cowman]

I have 2 altimeters now so I could do this with one and leave the other on MSL... but I won't. Seems like a good way to create confusion.