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Aircraft Systems > AS 17 - Intro GPS 3 > Flashcards

AS 17 - Intro GPS 3 Flashcards

1
Q

Review Questions

What does the carrier tracking loop adjust for?

A

Doppler shift due to the relative motion of the satellite and receiver.

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2
Q

Review Questions

What carrier frequency band(s) is the C/A code broadcast on?

A

L1 Band

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3
Q

Review Questions

What carrier frequency band(s) is the P code broadcast on?

A

Both L1 and L2

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4
Q

Overall, GPS error is a combination of which two types of errors?

A

Measurement of the distance from the satellite to the receiver

Having less than perfect fix geometry

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5
Q

The error, measurement of the distance from the satellite to the receiver, is also known as what?

A

User Range Error (URE)

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6
Q

The error, having less than perfect fix geometry, is also known as what?

A

Dilution of Precision (DoP)

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7
Q

URE error comes from which sources?

A

Satellite, ground control segment or the receiver.

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8
Q

Describe the Satellite clock drift error.

A

It is the error associated with each individual satellite.

Satellite time is updated every 8 hours, so the error should not exceed 2 meters 95% of the time

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9
Q

What is responsible for Control Segment Errors? What error will it produce?

A

Inaccurate ephemeris data caused by inaccurate positioning of the satellite by the ground station.
Will give errors up to 2.5 m 95% of the time over an 8 hour period

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10
Q

What errors make up the largest portion of UREs?

A

Receiver errors

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11
Q

What is the largest overall cause of GPS error?

A

Atmospheric modeling

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12
Q

What is atmospheric modeling?

A

When the GPS signal undergoes refraction as it passes through the ionosphere and troposphere.
The refraction increases the path length, generating an error.

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13
Q

Total URE for the P code and C/A code is expected to be what?

A

P code: up to 6.6m 95% of the time

C/A code: up to 13.9m 95% of the time

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14
Q

Describe Multi-path error, how is it similar to the Atmospheric Modeling error?

A

Occurs as the GPS signal is reflected off other surfaces before reaching the User Segment antenna. Similar in that it increases the path length of the signal, inducing errors.

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15
Q

What causes the Dilution of Precision error?

A

Having a fix geometry less than 90°

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16
Q

True or false

While airbourne, we are concerned with 2 dimensional position error

A

False, while airbourne, we are concerned with 3 dimensional position error.

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17
Q

DoP is considered to be a coefficient of ____, 95% of the time.

A

2.54

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18
Q

How is total system accuracy calculated?

A

DOP x URE = Total system accuracy, 95% of the time

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19
Q

What is the total system accuracy for the P code?

A

DOP x URE

2.54 x 6.6 = 16.8 m, 95% of the time

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20
Q

What is the total system accuracy for the C/A code?

A

DOP x URE

2.54 x 13.9 = 35.3 m, 95% of the time

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21
Q

How does a sequential receiver work?

A

They have at least one channel and track a single satellite then switch to the next satellite.

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22
Q

A multiplex receiver has how many hardware and software channels?

A

Normally two hardware and multiple software channels.

23
Q

A multiplex receiver can sample four satellites in how much time?

A

20 milliseconds

24
Q

Describe a Continuous Receiver

A

Has four or more channels that allow for continuous tracking of four or more satellites.

25
Q

What does a Differential GPS use to eliminate errors associated with GPS?

A

Ground reference stations.

26
Q

How accurate is DGPS?

A

Accurate to 1m.

27
Q

What are the two DGPS systems?

A

LAAS and WAAS

28
Q

LAAS and WAAS are what type of systems?

A

Ground and space

29
Q

LAAS focuses its service where?

A

Airport areas.

30
Q

How does the LAAS communicate and what does it communicate?

A

Its communicates with the plane via a BHF radio data link from a ground based transmitter and it broadcasts airport corrections and data for error bounding.

31
Q

What kind of approaches is LAAS used for?

A

Standard RNAV approaches

32
Q

What specifics are not required with LAAS?

A

No specific pilots qualifications
No specific frequencies need to be dialed up
No unique aircraft equipment needed

33
Q

What is required with a LAAS, but not WAAS?

A

RAIM checks

34
Q

What does the WAAS network consist of?

A

A network of approximate 25 ground reference stations.

35
Q

Describe the process for any corrections noted by the WAAS.

A

Signals from the GPS satellites are received by ground reference stations.
These signals are evaluated for errors, if any are found a correction message is sent to a geosynchronous satellite via a ground uplink system.
The message is then broadcast on the same freq as the GPS signal to any receiver onboard an aircraft within the WAAS coverage area.

Signal> Ground Reference Receivers> Geosynchronous Communication Satellite> Receiver aboard AC = correction received

36
Q

What are some caveats with WAAS?

A

Aircraft must have a WAAS capable FMS
Both pilots must be qualified to fly a WAAS enabled RNAV approach
Specific channel is required.

37
Q

Where would a specific WAAS channel be found?

A

GPH 200, in top let corner of plate

38
Q

Is a RAIM check required for a WAAS?

A

No

39
Q

If WAAS is unavailable, what is the default?

A

LAAS

40
Q

The CT 142 GPS has which type of receiver?

A

Single channel rapid sequencing C/A code receiver

41
Q

What does the Emulated GPS receive inputs from?

A

Aircraft GPS (UNS-1C)

Inertial Reference Unit

42
Q

What inputs does the Aircraft GPS (UNS-1C) provide the Emulated GPS?

A 
Px 
Time
Satellite information
System status
Altitude
G/S
Ground Track
43
Q

What inputs does the DADC, via the IRU, provide the Emulated GPS?

A

TAS

44
Q

What does the Emulated GPS provide the User Interface?

A 
Px 
Time
Satellite info
Altitude
Ground track
Ground speed
TAS
45
Q

True or false

The six emulated GPS aboard the CT 142 are capable of initialization, data entry and navigation. Additionally, it maintains its own database of nav info.

A

True

46
Q

True or false

The emulated GPS does not represent the actual status and current data of the aircraft GPS.

A

False, it does

47
Q

Regarding the Emulated GPS, 3 satellites provides:

A

Lat/Long

Altitude info no longer available

48
Q

Regarding the Emulated GPS, 2 satellites provides:

A

Lat/Long not available

GPS not available, revert to degraded ops

49
Q

What happens if the GPS has failed?

A

GPS position becomes erratic and varies randomly with large errors.
Time on NTS still operates

50
Q

Review Questions

What is URE?

A

User range error

An error in the measurement of the distance from satellite to receiver

51
Q

Review Questions

Regarding URE, what are the sources of error for satellite, control and receiver errors?

A 
Satellite: Time error
Control: Ephemeris
Receiver: Ionosphere
                 Troposphere
                 Multipath
52
Q

Review Questions

What is DOP?

A

Dilution of precision (less than perfect geometry)

53
Q

Review Questions

What is the largest source of error for GPS

A

Receiver: Atmospheric refraction and modeling

Aircraft Systems (19 decks)

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