Heathrow and altitude fix at 6,000ft?
Discussion
bennyboydurham said:
climbing to the heights either as per the chart (3000, 4000 and 6000 feet in the case of the MID4F SID off runway 27R)
A few minor points:The figures quoted are Altitudes since they are QNH based and not Heights (which would be QFE based).
If you look at the SID you will notice the figures 3000, 4000, and 5000 are under-lined. This means that, at the relevant radial/range you are not to be below that altitude but you can be above. Indeed if you read the notes at the bottom of the Plate this is expanded upon.
You will notice that the 6000 figure at MID is both under-lined and over-lined. This means that you are to be at 6000', neither above nor below.
You will also notice that this is the Transition Altitude, upon climbing through which you set 1013.25 on the Altimeters.
bennyboydurham said:
You'll have been on a SID, or Standard Instrument Departure. In essence, these are standard routings to get traffic from the departure runway to the point at which they continue the journey under their own navigation. Imagine them as slip roads in the sky to the motorway entry point. So, let's say the first point on your flight plan is the navigation beacon at Midhurst VOR in Sussex. Your pilot will be assigned one of the following four SIDs according to whichever runway is in use, punch that into the flight management computer and then after takeoff follow that track, climbing to the heights either as per the chart (3000, 4000 and 6000 feet in the case of the MID4F SID off runway 27R) or will receive instructions from ATC giving him headings and altitudes which over-ride those on the chart. When your pilot gets to the MID beacon he'll be told by ATC to 'resume own navigation' which means the aircraft is cleared along the series of beacons and waypoints that make up the route and will no longer receive directions from ATC, apart from altitude restrictions for other traffic.
In reality aircraft usually fly the first part of the SID and then are given vectors (directions) by ATC. Smaller airfields don't use SIDs at all, and simply direct traffic out away from the airport via radar coverage.
A minor point, but the unless the aircraft is assigned a heading by ATC, they are already under their own navigation. The SID will be part of the planned route, so if the crew are left alone, they'll just go to the next point on the route after MID, and there's no need to be instructed 'resume own nav'.In reality aircraft usually fly the first part of the SID and then are given vectors (directions) by ATC. Smaller airfields don't use SIDs at all, and simply direct traffic out away from the airport via radar coverage.
At quieter airports there tends to be a lot of pressure to keep things climbing/descending without leveling, to try and reduce fuel burn etc. When the intensity of traffic is as high as places such as LHR etc, you just have to accept that things are going to level off. I suggest the OP goes flying on a quiet day from a quiet airport - I once coordinated a higher level from an en route sector for a departing aircraft which was passing about 3000ft, and the first instruction they got was "Climb now, Flight Level 330" (their cruising altitude/level). I think it's fair to say no one had many aeroplanes to work with that day.
Ginetta G15 Girl said:
You will also notice that this is the Transition Altitude, upon climbing through which you set 1013.25 on the Altimeters.
I assume that's the barometric setting so that all the aircraft in the area show the same altitude?Is it set when flying at 6,000ft or only when you go above? ie in the OP would they have set it while holding at 6,000ft before continuing the climb?
The standard pressure setting of 1013 is set so that local pressure variations become irrelevant. When you have that set and are above the transition altitude, your vertical distance is referred to as a Flight Level. Aircraft maintaining, let's say, Flight Level 100 (i.e. 10,000 ft from the datum of 1013 HPa) may move closer to or further away from sea level, because they will pass through areas of relatively high or low pressure. An aircraft maintaining 3000 feet altitude, i.e. vertical distance from sea level, will have to adjust the pressure setting of their altimeter as required so that they don't move around relative to sea level. The QNH will be broadcast by ATC when it changes, or when an aircraft first contacts the frequency. I may not have explained that very well.
As GG15G said, the SID chart indicates a restriction of neither above nor below 6000' at one point, so 1013 is only set once climb is given above the transition altitude. If you are at 6000', you stay on the QNH until climbing further.
As GG15G said, the SID chart indicates a restriction of neither above nor below 6000' at one point, so 1013 is only set once climb is given above the transition altitude. If you are at 6000', you stay on the QNH until climbing further.
Prawo Jazdy said:
The standard pressure setting of 1013 is set so that local pressure variations become irrelevant. When you have that set and are above the transition altitude, your vertical distance is referred to as a Flight Level. Aircraft maintaining, let's say, Flight Level 100 (i.e. 10,000 ft from the datum of 1013 HPa) may move closer to or further away from sea level, because they will pass through areas of relatively high or low pressure. An aircraft maintaining 3000 feet altitude, i.e. vertical distance from sea level, will have to adjust the pressure setting of their altimeter as required so that they don't move around relative to sea level. The QNH will be broadcast by ATC when it changes, or when an aircraft first contacts the frequency. I may not have explained that very well.
As GG15G said, the SID chart indicates a restriction of neither above nor below 6000' at one point, so 1013 is only set once climb is given above the transition altitude. If you are at 6000', you stay on the QNH until climbing further.
Ta, I understood what the setting did roughly. But thanks for explaining the transition.As GG15G said, the SID chart indicates a restriction of neither above nor below 6000' at one point, so 1013 is only set once climb is given above the transition altitude. If you are at 6000', you stay on the QNH until climbing further.
To extend from what Prawo said:
There are basically 4 altimeter settings, these being: QFE, QNH, RPS, and Standard Altimeter.
QFE is not generally used in Civil Aviation outside of General Aviation (ie Light a/c), although it is used by the RAF Fast Jet and Training types, and is the baro setting whereby the altimeter will read zero at touchdown for a given airfield. It is obviously of benefit to the ab initio pilot because QFE instantly tells you how high you are above the airfield.
QNH is the baro setting whereby the altimeter would read zero at sea level. QNH is airfield based, thus if the airfield in question was at sea level the altimeter would read zero, otherwise it will give you your height above sea level at touchdown. Thus, to work out your circuit height or Instrument Approach Minima you have to subtract the airfield elevation from the altimeter reading - not ideal for baby pilots (or Tornado Crews)!
The reason why QNH is just about universal in the 'real' world is because you may be flying to an airfield that is so high it would be physically impossible to set a QFE - eg Nairobi.
RPS (or Regional Pressure Setting) is a forecast Regional QNH rounded down that is valid for the next hour. Thus this is a QNH that is the lowest for a given area. It is what we would set on our altimeters when operating at low level because it gives you an idea of how high the terrain is around your flightpath. Pretty useful if you have to make a bad weather abort from low level!
Standard Altimeter is a baro setting of 1013.25 millibars. Above the Transition Altitude (TA) every a/c will have this set, thus vertical separation is easy to achieve because everyone is working to the same datum. Below this then people will be on QNH or QFE in the Terminal Manoeuvring Areas as directed.
Generally speaking, in the UK the Transition Altitude is 3000 ft. However in certain pieces of controlled airspace such as around Heathrow the TA is set higher (6000 ft) because it allows a greater buffer where the airspace is busy for manoeuvring a/c. In the USA the TA is 18,000 ft across the entire country.
Obviously there must be a 'safety boundary' around TA to take account of a/c climbing and setting 1013 and a/c descending and setting QNH/QFE as appropriate. This is known as the Transition Layer and extends between the Transition Altitude and the Transition Level (TL), the latter being the lowest useable Quadrantal Flight Level above the Transition Altitude - to all intents and purposes in the UK this is around 500 ft. Ie the TA is 3000 ft, the TL is Flight Level 035 (based on 1013 this is about 3500 ft on an average day).
There are basically 4 altimeter settings, these being: QFE, QNH, RPS, and Standard Altimeter.
QFE is not generally used in Civil Aviation outside of General Aviation (ie Light a/c), although it is used by the RAF Fast Jet and Training types, and is the baro setting whereby the altimeter will read zero at touchdown for a given airfield. It is obviously of benefit to the ab initio pilot because QFE instantly tells you how high you are above the airfield.
QNH is the baro setting whereby the altimeter would read zero at sea level. QNH is airfield based, thus if the airfield in question was at sea level the altimeter would read zero, otherwise it will give you your height above sea level at touchdown. Thus, to work out your circuit height or Instrument Approach Minima you have to subtract the airfield elevation from the altimeter reading - not ideal for baby pilots (or Tornado Crews)!
The reason why QNH is just about universal in the 'real' world is because you may be flying to an airfield that is so high it would be physically impossible to set a QFE - eg Nairobi.
RPS (or Regional Pressure Setting) is a forecast Regional QNH rounded down that is valid for the next hour. Thus this is a QNH that is the lowest for a given area. It is what we would set on our altimeters when operating at low level because it gives you an idea of how high the terrain is around your flightpath. Pretty useful if you have to make a bad weather abort from low level!
Standard Altimeter is a baro setting of 1013.25 millibars. Above the Transition Altitude (TA) every a/c will have this set, thus vertical separation is easy to achieve because everyone is working to the same datum. Below this then people will be on QNH or QFE in the Terminal Manoeuvring Areas as directed.
Generally speaking, in the UK the Transition Altitude is 3000 ft. However in certain pieces of controlled airspace such as around Heathrow the TA is set higher (6000 ft) because it allows a greater buffer where the airspace is busy for manoeuvring a/c. In the USA the TA is 18,000 ft across the entire country.
Obviously there must be a 'safety boundary' around TA to take account of a/c climbing and setting 1013 and a/c descending and setting QNH/QFE as appropriate. This is known as the Transition Layer and extends between the Transition Altitude and the Transition Level (TL), the latter being the lowest useable Quadrantal Flight Level above the Transition Altitude - to all intents and purposes in the UK this is around 500 ft. Ie the TA is 3000 ft, the TL is Flight Level 035 (based on 1013 this is about 3500 ft on an average day).
magpie215 said:
Ginetta G15 Girl said:
in the UK the Transition Altitude is 3000 ft.
Talk of the TA being increased to 16,000ft Europe wide, Also going semi circular rule only no quadrantle.HARMONISATION OF SOUTH EAST ENGLAND TRANSITION ALTITUDE
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