Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

ATPL - BGS [Mod 1] Meteorology > 02. Altimetry > Flashcards

02. Altimetry Flashcards

1
Q

Altimetry

“The reading of a station pressure taken on an accurate barometer and adjusted for any difference in height between the barometer and the field elevation. Should read zero on the ground on the altimeter”

This is a definition of which pressure setting

A

QFE

1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Altimetry

“The station pressure adjusted down to mean sea level (MSL) using ISA values for the temperature between the station at the field elevation and MSL. Since the altimeter uses ISA values, it should read the same as teh station elevation on the ground from MSL”

This is a definition of which pressure setting

A

QNH

1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Altimetry

“Above a set altitude call the transition altitude, aircraft operate with on this pressure of 1013 hPa, sometimes referred to as the ‘pressure setting’”

This is a definition of which pressure setting

A

STANDARD PRESSURE

1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Altimetry

“the station pressure adjusted down to MSL using actual station temperature and the actual lapse rate”

This is a definition of which pressure setting

A

QFF

2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Altimetry

The RPS pressure setting is given to pilots based on what 2 parameters

RPS - Regional Pressure Setting

A
  1. LOWEST forecast for region
  2. 1 HOUR AHEAD

2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Altimetry

What does ASR and RPS stand for

A
  1. ALTIMETER SETTING REGION
  2. REGIONAL PRESSURE SETTING

2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Altimetry

Airfield QFE pressure is given from what point

A

HIGHEST POINT ON AIRFIELD SURFACE

2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Altimetry

If the touchdown point of a runway is significantly below the airfield QFE, what may be issued to pilots

A

TOUCHDOWN QFE

2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Altimetry

“the touchdown height that will be indicated on the altimeter if the standard setting of 1013 hPa is set on the altimeter. Used at high airfields where QFE woudl be too low a value to set on the altimeter subscale”

This is a defintiion of what pressure setting

A

QNE

3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Altimetry

For stations ABOVE sea level;

  1. If temperature is warmer than ISA, then QNH is MORE or LESS than QFF
  2. If temperature is COLDER than ISA, then QNH is MORE or LESS than QFF
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Altimetry

For stations BELOW sea level;

  1. If temperature is warmer than ISA, then QNH is MORE or LESS than QFF
  2. If temperature is COLDER than ISA, then QNH is MORE or LESS than QFF
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Altimetry

If your QNH was 1011 and you are instructed the pressure setting is now QNH 1025 and you change the kollseman window to the new pressure setting, has your altitude INCREASED or DECREASED

A

INCREASED

REMEMBER

“WIND ON pressure, WIND ON altitude”

“WIND OFF pressure, WIND OFF altitude”

MEMORY AID

4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Altimetry

When flying high pressure to low pressure, what will the altimeter read

A

OVER READ
Lower than you think you are

REMEMBER
* HIGH to low, watch out BELOW

MEMORY AID

6

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Altimetry

An aircraft departs an airfield (point A) at an altitude of 1500 m with the QND set to 1010 hPa. It arrives over a hill top (point B) where teh QNH is 990 hPa. The hill is 1000 m high. Assuming 8m per 1 hPa, what will the obstacle clearance be at point B

A

340 m

REMEMER
Always read the question. Typically you will give answers in feet, but in this instance, it is asking for meters!

  • Determine the barometric error
  • 1010 (point A as set on the subscale) - 999 (point B, where the obstacle is)
  • 1010 - 990 = 20 hPa
  • 20 hPa x 8m per hPa
  • 20 x 8 = 160 m
  • Since QNH was set at point A, and we know QNH for the airfield is taken from the station at the airfield, the QNH altitude at the airfield must be the same as the airfield altitude, in this instance 1500 m
  • The QNH at point B is LESS than at point 1, meaning we need to WIND OFF PRESSURE (which means WIND OFF ALTITUDE)
  • 1500 - 160 = 1340m
  • The elevation of the hill is 1000 m and the aircraft is flying at 1340 m
  • 1340 - 1000 = 340 m Clearance

8

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Altimetry

An aircraft is at FL40. What is the AMSL altitude if QNH is 998 hPa

A

3595 ft

REMEMBER
Always read the question. The first piece of information is that the aircraft is flying a FLIGHT LEVEL i.e. FL40. This means it must be using the standard pressure setting of 1013.
* Determine the barometric error
* Aircraft is flying a FLIGHT LEVEL so is on the standard pressure setting, which is 1013
* The QNH at the given point is 998 hPa
* 1013 - 998 = 15 hPa
* the QNH is LESS than the standard pressure setting, so WIND OFF pressure, WIND OFF altitude
* Determine how much altitude to we will lose
* 15 hPa x 27 ft per hPa (NOTE typically exams are now using 30 ft per hPa)
* 15 x 27 = 405 ft
* 4000 - 405 = 3595 ft

DIAGRAM

9

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Altimetry

If the OAT temperature differs from ISA, this will cause either an OVER READ or an UNDER READ on the altimeter. This is known as what

A

TEMPERATURE ERROR

10

17
Q

Altimetry

If the OAT is warmer than ISA, the true altitude will be MORE or LESS than indicated altitude

A

MORE
TRUE > indicated

TEMPERATURE ERROR

ERROR CORRECTION

10

18
Q

Altimetry

If the OAT is colder than ISA, the true altitude will be MORE or LESS than indicated altitude

A

LESS
true < INDICATED

For every

TEMPERATURE ERROR
​
ERROR CORRECTION
​
10

19
Q

Altimetry

What is the equation for working out temperature error correction

A

4 x HEIGHT (in thousands of feet) x ISA DEVIATION
for every 1℃ ISA Dev, 4ft for every 1000 ft

NOTE height is the indicated altitude AFTER any barometric correction plus or minus the elevation of teh station at which the pressure is measured

ERROR CORRECTION

11

20
Q

Altimetry

You are flying at FL200. OAT is -40℃ and the pressure at sea level is 1033 hPa. What is the true altitude

A

19,308 ft
DIAGRAM

BAROMETRIC ERROR
* Start with the barometric error.
* We are flying a flight level, meaning we must be flying the standard pressure setting, which is 1013
* The given QNH is 1033
* 1033 - 1013 = 20 hPa
* Given QNH is ABOVE the SPS setting, WIND ON pressure, WIND ON altitude
* 20 hPa x 27 ft per 1 hPa = 540
* Flying at FL200 so 20,000 ft
* 20,000 + 540 = 20,540 ft is aircrafts altitude
ISA DEVIATION
* Determine ISA deviation with 15 - (alt x 2) - OAT
* 15 - (20 x 2)
* 15 - 40 = -25℃
* Given OAT is -40℃
* -25℃ - -40℃ = -15℃
TEMPERATURE ERROR CORRECTION
* Use the formaul 4 x height (thousands of feet) x ISA deviation
* 4 x 20.54 x -15 = -1232.4
* The OAT is COLDER than ISA, so the altimeter will OVER READ - example
DETERMINE TRUE ALTITUDE
* 20,540 - 1232 = 19,308 ft

12

21
Q

Altimetry

QNH is calculated from station pressure, so therefore assumes what conditions.

A

ISA

13

22
Q

Altimetry

As a result of QNH being calculated from an airfield station based on ISA conditions, and QFF being calculated based on actual sea level pressure, what does this mean in regards to the relationship between QNH and QFF if the temperature deviates from ISA conditions

A

QNH and QFF WILL DIFFER

QNH vs QFF MEMORY AID

QNH vs QFF DIAGRAM

13

23
Q

Altimetry

What is the equation to determine QFE from QNH

If QFE is 1001 at 200 ft, what is QNH

A

QNH = QFE + (ELEVATION / 27 )
QNH = QFE (hPa) + (elevation / 27 ft per 1 hPa difference)

If QFE is 1001 at 200 ft, what is QNH
* 1001 + (200 / 27)
* 1001 + 7
* QNH = 1008 hPa

15

24
Q

Altimetry

What is the equation to determine QFE from QNH

If QNH is 1008 at an airfield elevation of 200 ft, what is QFE

A

QFE = QNH - (ELEVATION / 27 )

If QFE is 1001 at 200 ft, what is QNH
* 1008 + (200 / 27)
* 1008 - 7
* QNH = 1001 hPa

15

25
Q

Altimetry

If you fly from a higher temperature to a low temperature, the altimeter will OVER READ or UNDER READ

A

OVER READ

REMEMBER
* When temperature is LOW, aircraft is LOWER than you think you are

DIAGRAM

15

26
Q

Altimetry

If you fly from a low temperature to a high temperature, the altimeter will OVER READ or UNDER READ

A

UNDER READ

REMEMBER
* When temperature is HIGH, aircraft is HIGHER than you think you are

DIAGRAM

15

27
Q

Altimetry

An aircraft is making a precision approach to an aerodrome at 4000 ft amsl at an OAT of -30℃. The decision altitude (DA) is QNH based at 4200 ft, the decision height (DH) is 200 ft above touchdown. Use the table to determine the correct indicated altitude of decision height.

A

4240 ft

TABLE

  • We are given the selected datum and height above to making a decision at decision height
  • Datum for DA is 4200 ft and the decision height (DH) is 200 ft above
  • Find the 200 ft column, cross reference to the given tempreature of -30℃
  • We can see that we need to add 40ft
  • 4200 + 40 = 4240 ft

16

28
Q

Altimetry

In the Northern Hemisphere, what direction does the wind flow in a low pressure system

A

ANTI-CLOCKWISE

17

29
Q

Altimetry

In the Northern Hemisphere, what direction does the wind flow in a high pressure system

A

CLOCKWISE

17

30
Q

Altimetry

An aircraft travelling from a high pressure system into a low pressure system in the Northern Hemisphere will experience drift in which direction

A

STARBOARD or RIGHT

REMEMBER
* Wind in your back, LOW is to the LEFT
or;
* Face the wind, you are LEFT HIGH AND DRY (indicating high is to your left*

EXAMPLE

17

31
Q

Altimetry

You are intending to fly along an airway where the minimum flight level given on teh chart is FL150

The highest ground you will over is 12,000 ft and the MOCA on the chart is shown as 14,000 ft.

The temperature at FL150 is -25℃ and the local QNH, measured at an airfield where the elevation is 1500 ft AMSL is 993 hPa.

What is the lowest usable Flight Level to conform with the published MOCA?

MOCA = Minimum Obstacle Clearance Altitude

A

FL160

BAROMETRIC ERROR
* Calculate the barometric error first. We are at FL150 ⋉ 15,000 ft. FL means we are on SPS of 1013.
* Local QNH is given as 993. We know that 993 is LOWER than 1013, WIND OFF pressure, WIND OFF altitude
* (1013 - 993) x 27 ft per 1 hPa
* 20 x 27 = 540 ft
* WIND OFF pressure, WIND OFF altitude, 15,000 - 540
* 14,460 ft
ISA DEVIATION
* OAT is given as -25℃
* calculate what temperature would be under ISA conditions at same altitude
* 15 - (alt x 2) ⋉ 15 - (15 x 2)
* 15 - 30 = -15℃
* Deviation is (-15) - (-25)
* 10℃
** TEMPERATURE CORRECTION**
* OAT is COLDER than ISA, so we are OVRE READING, meaning we must subtract
* Use formula to determine the correction, 4 x (alt in thousands of feed) x ISA deviation
* ⋉ 4 x 14.46 x (-10)
* -519 (rounded up)
TRUE ALTITUDE
* We now subtract the temperature correction from the barometric error corrected altitude
* 14,460 - 519
* ** 13,941 ft**

This altitude is BELOW the MOCA of FL140.
We are already flying at FL150 so it means we must fly at a HIGHER FL to maintain the MOCA

FL160

18

32
Q

Altimetry

Why does airflow over high ground affect the atmospheric pressure?
What is the affect?

Think similar to airflow over the top of a wing

A
  1. BERNOULLI EFFECT
  2. DROP IN PRESSURE

  • As air stream is forced up and over the hill top, the air streams get closer together
  • Bernoulli’s therom tells us that P1 + P2 = P3, i.e. dynamic pressure + static pressure = Total pressure
  • The pressure remains constant through a tube, so when the tube becomes thinner, the flow at which it passes through will speed up
  • Static pressure will drop in other words, and dynamic pressure will increase

19

33
Q

Altimetry

“The altitude in the ISA at which the air density would be equal to the actual air densitiy at the place of observation”

This is a definition of what altitude

A

DENSITY ALTITUDE

  • If I am flying at 15,000 ft, is the density equivilant to what we expect it to be at 15,000 ft?
  • The density may be more, or it may be less
  • Therefore, if the outside density was equivilant to 13,000 ft, despite being at 15,000 ft, the aircraft would perform as though it were at 13,000 ft.

19

34
Q

Altimetry

What is the equation to determine the pressure altitude

A

PA = Elevation + (( 1013 - QNH) x27 )

REMEMER
* Pressure altitude is SPS setting, hence 1013
* If QNH was given at airfield as 1009 hPa at 1500ft
* PA = 1500 + ((1013 - 1009) x 27)
* 1500 + (4 x 27)
* 1500 + 108
* ** PA = 1608 ft**

35
Q

Altimetry

What is the equation to determine Density Altitude

A

DA = PA + (ISA Deviation x 120)
⋉
DA = PA + (Ambient Temp - 15)

REMEMBER
* Pressure altitude is SPS setting of 1013 hPa, therefore a Flight Level
* Aircraft at FL100 and OAT -35℃, what is DA
* 10,000 + (ISA DEV x 120)
* ISA Dev is 15 - (alt x 2) - OAT
* 15 - (10 x 2) - -35℃
* 15 - 20 = -5℃
* -5℃ - -35℃
* -30℃
* 10,000 + (ISA DEV x 120) ⋉ 10,000 + (-30℃ x 120)
* -3600 ft
* DA = 10,000 - 3600
* 6400 ft

20

36
Q

Altimetry

What is the equation to determine Density Altitude using an ISA deviation

A

ATPL - BGS [Mod 1] Meteorology (27 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions