Ask The Pilot

[straitman]

How accurate is GPS in terms of vertical separation? Given every measurement/measuring device is subject to a degree of error, how close would 2 planes likely come if they were travelling at '1000ft vertical separation'?

GPS is not used for vertical separation.

 

[flychrisfly]

GPS is not used for vertical separation.

Okay, thanks. In that case my question becomes:
How accurate are the measurements for vertical separation? Given every measurement/measuring device is subject to a degree of error, how close would 2 planes likely come if they were travelling at '1000ft vertical separation'?

 

[straitman]

Okay, thanks. In that case my question becomes:
How accurate are the measurements for vertical separation? Given every measurement/measuring device is subject to a degree of error, how close would 2 planes likely come if they were travelling at '1000ft vertical separation'?

Each aircraft operating in the same airspace has their altimeters set to the same standard pressure.

Area pressure below 10,000 ft and 1013Mb above 10,000 ft. Altimeters are checked on taxi to be within certain tolerances. (Used to be +15 to -85 ft though that may be old hat now)

Airborne they also have tolerances though I cannot recall what they are. Probably more importantly is that there are minimum separation altitudes applied which negate any issues.

Someone more current than me should be able to elaborate.

 

[por930]

Okay, thanks. In that case my question becomes:
How accurate are the measurements for vertical separation? Given every measurement/measuring device is subject to a degree of error, how close would 2 planes likely come if they were travelling at '1000ft vertical separation'?

This is an interesting link that may address your question: Airspace RVSM There are operating altitude differences these rules apply to in the various countries airspaces, though between FL 290 and FL410 seems common.

An extract...."An automatic altitude control system should be required, and it should be capable of controlling altitude within ±65 ft (±20 m) about the acquired altitude when operated in straight and level flight under non turbulent, non gust conditions." They also go on to say, "The RVSM tolerance seems to be specified as tight as 80 feet but then gets confused with additives of standard deviation that bring that number as high as 245 feet.

My flights never extended this high, but I am sure the jet boys will have this all under control.

 

[harvyk]

Each aircraft operating in the same airspace has their altimeters set to the same standard pressure.

Area pressure below 10,000 ft and 1013Mb above 10,000 ft. Altimeters are checked on taxi to be within certain tolerances. (Used to be +15 to -85 ft though that may be old hat now)

Airborne they also have tolerances though I cannot recall what they are. Probably more importantly is that there are minimum separation altitudes applied which negate any issues.

Someone more current than me should be able to elaborate.

Only 10,000ft for standard pressure? I was under the impression that standard pressure came into play at FL180. Or is that a US thing which the flight sims use?

 

[Orca]

Only 10,000ft for standard pressure? I was under the impression that standard pressure came into play at FL180. Or is that a US thing which the flight sims use?

Transition altitude varies around the world. Relatively low here in Aus due to lack of mountains/high terrain. You're correct re:18,000 ft being used across USA and Canada. Indeed in some places it can be as low as 3 or 4 thousand feet

 

[harvyk]

Transition layer/altitude varies around the world. Relatively low here in Aus due to lack of mountains/high terrain.

Follow up question then for those whom fly 747's (and I'd imagine other types, although I'm not familiar with other flight decks). In the simulator I'm building, it has a standard altitude button for flying over FL180. Pressing the button below FL180 will switch to standard mode, but the standard mode wording will be in yellow until above FL180. When setting the altimeter manually, below FL180 the numbers will be in green, but above FL180 they will be in yellow. I'm guessing yellow is simply a warning to state you're not in the right mode.

Is this how an actual jumbo shows colours? Could this functionality be different depending on the operator?

 

[jb747]

The aircraft know where in the world they are, and they know the normal transition altitudes. They get upset if you don't change modes when they expect it.

It hasn't been automated or standardised yet because neither the terrain, the pressure, nor the temperature fall into exact models.

 

[Saab34]

What's the procedure if you wish to depart past Sydney curfew and does it normally get granted? Do you need to call ops or something? I always thought there was no option otherwise everyone would abuse it.

Flew Jetstar last week we started boarding at 1058pm and I quizzed the agent and she said 'The Captain will sort out the Curfew problem'. Needless to say we pushed back at 1120pm and nothing was ever mentioned.

 

[AviatorInsight]

Follow up question then for those whom fly 747's (and I'd imagine other types, although I'm not familiar with other flight decks). In the simulator I'm building, it has a standard altitude button for flying over FL180. Pressing the button below FL180 will switch to standard mode, but the standard mode wording will be in yellow until above FL180. When setting the altimeter manually, below FL180 the numbers will be in green, but above FL180 they will be in yellow. I'm guessing yellow is simply a warning to state you're not in the right mode.

Is this how an actual jumbo shows colours? Could this functionality be different depending on the operator?

While I can't speak for the jumbo (although I imagine that's how most Boeings work), it's exactly how the B777 operates. Once you pass transition and haven't set the correct QNH it will go amber on both PFDs until you push that STD button where it will then revert to green.

Like JB said, aircraft know where they are in the world, and you tell it where it is during pre flight. Remember the set initial pos line? Then you'd put in your route...DEP..ARR, etc. The only thing you need to remember to do is flick the switch over yourself from inches to hectopascals once in the Oakland FIR (going to the US).

 

[jb747]

What's the procedure if you wish to depart past Sydney curfew and does it normally get granted? Do you need to call ops or something? I always thought there was no option otherwise everyone would abuse it.

Flew Jetstar last week we started boarding at 1058pm and I quizzed the agent and she said 'The Captain will sort out the Curfew problem'. Needless to say we pushed back at 1120pm and nothing was ever mentioned.

You call the company ops. It's their problem to sort out.

Unless there's been an unusual weather or airfield event, it will not normally be granted. The fines for breaching it are very large (in the range of half a million dollars). ATC cannot approve anything to do with the curfew.

 

[Dannyism]

When I was younger I knew someone who was studying/training to be a pilot. When we were at parties they were very very concerned about second hand smoke... Yes you know the variety I mean...

My questions are. Are their routine drug tests for commercial pilots? Are they urine, blood, saliva, hair or other? What happens if you return a positive?

 

[AviatorInsight]

When I was younger I knew someone who was studying/training to be a pilot. When we were at parties they were very very concerned about second hand smoke... Yes you know the variety I mean...

My questions are. Are their routine drug tests for commercial pilots? Are they urine, blood, saliva, hair or other? What happens if you return a positive?

I wouldn't call them routine, but I have been drug and alcohol tested at random, both at home base and at an outport. After any incident/accident, it is customary to be DAMP tested. It was a saliva test.

If it is found to be a positive test they then refer the case to the CASA medical review officer who will then make an assessment. But you are effectively stood down until it is proven that you are no longer under the influence.

 

[Dannyism]

I wouldn't call them routine, but I have been drug and alcohol tested at random, both at home base and at an outport. After any incident/accident, it is customary to be DAMP tested. It was a saliva test.

If it is found to be a positive test they then refer the case to the CASA medical review officer who will then make an assessment. But you are effectively stood down until it is proven that you are no longer under the influence.

Thank you for the reply. If a positive test for drugs or alcohol was determined to be correct, would your career be over? This was the source of concern for the friend in the story.

 

[docjames]

Re: comments upthread about wake turbulence.

Why is the 757 so more "wake inducing" than other aircraft (or similar / larger size)?

Is it left the pilots to assess nearby traffic and adjust or are there systems to predict / adjust?

It's not particularly pleasant from a pax seat - two notable instances IME were on a BA A320 AMS-LHR we hit a solid big pocket (captain reassuring on intercom about 5 seconds after, and crew were excellent doing lap of cabin checking on all pax and reassuring!) and another on takeoff with EK (A380) ex-DXB (screens suggested we were at a few thousand feet) - felt like about a 1-2 second (?relative) loss of lift - somewhat disconcerting on both occasions!

 

[AviatorInsight]

Thank you for the reply. If a positive test for drugs or alcohol was determined to be correct, would your career be over? This was the source of concern for the friend in the story.

I can't answer that. That would be up to the company to decide once they receive the report back from the medical review officer.

 

[AviatorInsight]

Re: comments upthread about wake turbulence.

Is it left the pilots to assess nearby traffic and adjust or are there systems to predict / adjust?

It's not particularly pleasant from a pax seat - two notable instances IME were on a BA A320 AMS-LHR we hit a solid big pocket (captain reassuring on intercom about 5 seconds after, and crew were excellent doing lap of cabin checking on all pax and reassuring!) and another on takeoff with EK (A380) ex-DXB (screens suggested we were at a few thousand feet) - felt like about a 1-2 second (?relative) loss of lift - somewhat disconcerting on both occasions!

There is always a necessity to see and avoid other traffic and that solely remains with the pilots regardless of any ATC clearances (think TCAS). There are no systems however to predict wake. This is left up to us to manage like I mentioned in an earlier post, a way to mitigate that would be to create an offset in the cruise.

I'm sure JB will be able to answer the comment re the 757.

 

[jb747]

Re: comments upthread about wake turbulence.

Why is the 757 so more "wake inducing" than other aircraft (or similar / larger size)?

I don't know that there is a definite answer to that. It was a early application of a supercritical wing design, that is very efficient, but also relatively small for the aircraft weight. The rotational velocity of the core is apparently about 50% faster than that of the much larger 767, designed at the same time.

Is it left the pilots to assess nearby traffic and adjust or are there systems to predict / adjust?

ATC try to handle it by use of spacing. Pilots just look at preceding aircraft and make an educated (or otherwise) guess.

It's not particularly pleasant from a pax seat - two notable instances IME were on a BA A320 AMS-LHR we hit a solid big pocket (captain reassuring on intercom about 5 seconds after, and crew were excellent doing lap of cabin checking on all pax and reassuring!) and another on takeoff with EK (A380) ex-DXB (screens suggested we were at a few thousand feet) - felt like about a 1-2 second (?relative) loss of lift - somewhat disconcerting on both occasions!

Neither of those sound like wake. No such thing as an air pocket either, nothwithstanding the media love of them.

If you cross the wake at an angle, it's very narrow, and passage lasts a fraction of a second. Tracking in the same direction will obviously give a much longer encounter, but the major result is a roll.

 

[docjames]

Well the captain described it as an "air pocket" from crossing aircraft - so i guess it was dumbed down for the SLF.

 

[iRobbo]

Re: comments upthread about wake turbulence.

Why is the 757 so more "wake inducing" than other aircraft (or similar / larger size)?

Is it left the pilots to assess nearby traffic and adjust or are there systems to predict / adjust?

It's not particularly pleasant from a pax seat - two notable instances IME were on a BA A320 AMS-LHR we hit a solid big pocket (captain reassuring on intercom about 5 seconds after, and crew were excellent doing lap of cabin checking on all pax and reassuring!) and another on takeoff with EK (A380) ex-DXB (screens suggested we were at a few thousand feet) - felt like about a 1-2 second (?relative) loss of lift - somewhat disconcerting on both occasions!

ATC apply Wake Turbulence Separation, lose the separation and you are stood down pending investigation, it is reported as a Breakdown of Separation i.e. a serious offence.

The 757 is an interesting one. The FAA has been investigating wake as a result of several incidents and accidents, some with the 757 as the lead aircraft, this was upon NTSB recommendations after investigations. They installed some Lidar radars at some airports (San Francisco, JFK were two I remember). They got a bunch of data from different distances from touchdown. Their findings were that the 757 was not to blame and there must have been other factors at play. They also determined it was the Wing rather than the Maximum Take Off Weight (MTOW) that determined the Wake (along with speed).

The upshot was that the FAA introduced what they call a 'Recat of wake turbulence' (recat being recategorization). It moved away from Heavy, Medium and Light and moved to a 7 category system, labelled from A (being the biggest wing i.e. A380) through to G, being the smaller wing. Most of what operates in Australian fell into the same Wake Turbulence separation standards as what is currently applied The big change was that the 757 went back to the equivalent of a current Medium. Currently in Australia we class a 757 as a Medium if following, but a Heavy if leading ( a 737 is a Medium for comparison). They introduced at airports they thought it would make an improvement in movement rates, and are selling the data collection to other agencies (I went to a presentation here, what I wrote above is based upon their presentation as I remember).

The other noteable piece was that they found the 737-800/900 wing had some 'interesting' Wake characteristics. I have had 3 Wake reports, all on left circuit ILS Runway 19 at BNE, all over water, all Mediums following 738's, all about 8-9 mn behind (there is no Wake Turbulence Separation for a Medium following a Medium, just the radar Separation of 3 nm is required), all several months apart. They all offset themselves (after seeking approval).

There was some talk of Australia introducing the Recat of Wake, we'll wait for the new ATC system to display the A-G instead of the H, M, L.