Help on FSL's ACARS Data Processing and Display

Updated 4 March 1998

You can display either graphical or textual ACARS data for approximately the past 30 days.

Plan-view plots

If the plot option is shown, ACARS data will be shown on a zoom-able, clickable map. The plot can show locations where data were taken, or wind barbs. Aircraft providing specific kinds of data can be selected

If g-measuring aircraft are selected, only data from aircraft that report (EXPERIMENTAL) vertical acceleration data will be shown. Colors range from black for zero incremental g's (smooth flight) to red for >= +/- 0.2 g's. Values greater than +/- 1.0 g's are coded with the bad data color.

If eddy dissipation rate measuring aircraft are selected, only data from aircraft that provide those (EXPERIMENTAL) variables will be shown. Colors are based on the maxium (not the median) e.d.r. reported, and range from black for zero (m^2/3/s) to red for >= 0.2. Hexidecimal values of 'FF' are coded with the bad data color.

If water-vapor-measuring aircraft are selected, only data from aircraft that have (EXPERIMENTAL) water vapor sensor will be shown.

Buttons below each map can be used to determine whether the next mouse click on the map will result in further zooming, generating a sounding, or in revealing the underlying ACARS data as text.

Soundings

If you choose the option to generate a sounding, you should then click on the map on a portion of a flight track that is ascending or descending. This will produce a skewt plot from the surface to approximately 400 mb generated by the aircraft on whose track you clicked.

Beneath the plot are some links.

The first link provides access to a skewt plot from the surface to 150 mb.
The second will generate a sounding from the MAPS analysis for the appropriate location and time. This may take 20 seconds or more to be produced. (MAPS analyses are generally available only for the past 16 or so hours.)
The third provides access to data from the sounding in the FAA 604 format used by the SHARP sounding analysis program.
The '?' link provides information on the FAA 604 format and SHARP.

Beneath these links is textual data for the sounding, followed by textual data for the entire flight track (within the originally-chosen time window) of the aircraft that generated the sounding.

The textual sounding data includes columns that show pressure altitude (in feet and standard-atmosphere millibars), a data descriptor ('DD'), wind direction and speed, temperature, dew point, water vapor mixing ratio ('WVMR'), and a vapor quality control flag ('WF'). Only a few aircraft currently provide vapor-related data, which is experimental. For details see the water vapor sensing system homepage.

Note that the pressure altitude indicated in the text may be greater or less than the actual airport altitude, depending on whether the pressure at the time of the sounding is less than or greater than that of the Standard Atmosphere.

The textual sounding data also shows Bng/Rng which is the Bearing (true) and Range (in nautical miles) of each data point from the airport. Also shown are time, latitude, longitude, and the station the report was routed through.

Textual Output

The format for textual data should be self-explanatory, except for g's, eddy, WVMR, WF, station and Flags.

- g's refers to the apparent acceleration due to gravity in the aircraft, in units of g. These values are provided by a few aircraft only, and should be centered around 1.

- eddy refers to eddy dissipation rate, in m^2/3/s. This is available from a few United aircraft. The median/maximum values are printed, for the time interval between observations (we think). Values flagged bad are coded as -9.99, which appears as asterisks.

- WVMR refers to Water Vapor Mixing Ratio, in g/Kg. This is available from a few aircraft on an experimental basis. For example, "5.67-2' corresponds to 5.67 x 10^-2 g/Kg. For details see the water vapor sensing system homepage.

- WF is the Water Vapor Mixing Ratio quality control flag:

'-' Missing data.
'0' Normal operations, Ground speed > 60 knots.
'1' Normal operations, nonmeasurement mode, Ground speed < 60 knots.
'2' Small RH, RH measured is < 1.5%;RH set to 1.5%.
'3' Humidity element is wet. RH at 5.0 volts for < 120 seconds.
'4' Humidity element contatminated. RH at 5.0 volts for > 120 seconds.
'5' Heater fail.
'6' Heater fail and wet/contatminated humidity element.
'7' Single validity bad. One or more of the input parameters for the mixing ratio calculation are invalid: TOT_PRESS, MACH TAT_WVSS, or RH. If RH is full scale, RH is considered valid to allow wet/contaminated status to be posted.
'8' Numeric error. Calculated mixing ratio at or above 10⁰, below 0.1^-9, or negative, or absolute value of denominator of calculations is less than 10^-15.
'9' Dew point is greater than temperature. (These values are plotted at the temperature value.)

- Station refers to the origin/reporting/destination airports listed in the report. The reporting airport refers to the ground station at which the particular observation was received, and is generally, but not always, an indication of the approximate location of the aircraft.

- Flags, one character each, report results of error tests, and whether data were interpolated and/or corrected. For error tests, 'p' means the test was passed, '-' means the test could not be performed, and capital letters designate various kinds of failure (see acars.h or testacars.c for details). Capital letters are associated with data that fail QC.

Data Descriptor. 'R' if reported temperature and wind were in appropriate ranges; 'T' if in addition tests for platform continuity were passed; 'X' if the data failed any test.
error Type. 'W' for wind, 'T' for temperature, 'B'for both.
flag for test 1 - temperature (see below)
flag for test 2 - wind direction (see below)
flag for test 3 - wind speed (see below)
flag for test 4 - platform speed(see below)
a blank (to guide the eye)
flag for test 5 - platform altitude 'bounce' (see below)
flag to indicate time was interpolated ('i'), or as reported ('r') (see below)
flag to indicate lat/lon was interpolated ('i'), or as reported ('r') (see below)
flag to indicate aircraft roll. 'G' means roll < 5 degrees, 'B' means roll > 5 degrees, '.' means not reported
a flag to indicate corrections, if any. (See details below.)
- 'r' for "raw" data,
- 'l' for data that has undergone lat/lon correction (other than interpolation),
- 'T' for data that has undergone temperature correction,
- 'f' for data that has had its longitude and wind direction flipped and its obs time set to the report receipt time,
- 't' for data that has had its obs time set to the report receipt time.

Notes on the tests:

This is output from routines that quality control "raw" acars data. Input is from the nimbus acars directory ascii acars data. Output is QCd acars data in netCDF. Currently (7/96) I perform the following tests and corrections.

TESTS:

(details of the tests)

1.temperature in range for altitude
2. wind direction in range 0-360, but different for UPS aircraft. see details.
3. wind speed > 0 and less than max for altitude, but different for Delta MD88 aircraft. see details.
4. aircraft groundspeed less than a certain value (currently 700 kts)
4a. aircraft lat or lon must be different between adjacent obs, if the altitude is different between the obs (the later ob is flagged bad).
5. "bounces" in aircraft altitude in any 3 adjacent obs must be less than a certain value (currently 38 feet per second).

CORRECTIONS

(loadacars.c performs these)

some aircraft report lat/lon in DDTTT (D=degrees, T=thousandths of a degree) instead of the expected DDMMt (D=degrees, M=minutes, t=tenths of minutes). The program discovers such aircraft (by looking for the last 3 digits of lat or lon having values of 600 or larger), maintains a list of the aircraft, and corrects the lat/lon. This is indicated by the correction flag l (the letter el).
some aircraft report temperature in degrees instead of tenths of degrees. The program uses a list of such aircraft (provided by hand) to correct these. This is indicated by the correction flag T (capitalized).
some aircraft (some Delta MD88s, on a list maintained by hand) have longitude flipped around -90 degrees West, have the v component of wind reversed, and have the u component of the wind stuck easterly (negative). The program uses a list of such aircraft (provided by hand) to "flip" the data, i.e., to correct the longitude and change the wind direction by 180 degrees. This is indicated by the correction flag f. (NOTE: this will still result in erroneous data when winds are actually from the east.) These aircraft have nearly all been fixed (3/98); only one aircraft still requires this correction, and it may be fixed at any time.
In addition, all Delta MD88s have the observation time set to the report receipt time, because they always report 0000 as the obs time. This is indicated by the corrected-flag t (lower case), ot f if the data have also been flipped.

INTERPOLATION OF TIME AND LAT/LON

Some high-resolution ascent/descent observations are reported without times, and/or lat/lon. In these cases:

time is interpolated by using DEFAULT values for expected time between observations , and
lat/lon is LINEARLY interpolated between known observation loaations.

DETAILS OF THE TESTS

=============== ACARS QC tests at FSL 29-Feb-1996 =================
TEMPERATURE:

Max temp:
if altitude > 35000 ft, T must be < -20 C
otherwise, T must be < 60 - 80 * (altitude/35000)

Min temp:
if altitude < 18000 ft, T must be > -60 C
if altitude > 35000 ft, t must be > -100 C
otherwise, t must be > -60 -40*(altitude - 18000)/17000

WIND:

direction:
For airlines other than UPS: 0 <= direction <= 360
For UPS, also allow -99 to -37, and -9 to 0 degrees. (Recent (8/96) evidence suggests wind directions of -36 to -18 are also good, but these are currently flagged as bad.)

speed (in knots):
speed >= 0
Also, for Delta MD88 aircraft, wind speeds of zero are flagged as bad (with bad wind speed flag = 'D').

and for the maximum speed, here's the C code:

    bad=0;
    if(altitude < 30000.) {
      wmax=70. + 230.* altitude / 30000.;
    } else if (ltitude < 40000.) {
      wmax = 300.;
    } else if (altitude < 45000.) {
      wmax = 300. - 100 * (altitude - 40000.) / 5000.;
    } else {
      wmax = 200.;
    }
    if(WindSpeed > wmax) {
      bad = 1;
    }

The remaining tests require a pair of observations. I assume reports from the same aircraft are unrelated if more than 20 minutes separates them.

Platform speed >= 0 (Must allow zero because sometimes the aircraft report from the ground, or circle.)

Platform speed <= 600 m/s (= 1099 kts) (This is faster than actual speeds because of the 1 minute time resolution on the observation time. Also, I use speed instead of change in lat/lon because the time between observations can vary.)

The following test requires three observations:

'Bounce' < 38 feet per second. ("Bounce" refers to an ascent followed by a descent, or vice versa. This test performs much better than simpler ascent/descent tests, because isolated bad observations that distort the altitude are relatively more common than step-function kinds of altitude errors.)

Prepared by Bill Moninger 303-497-6435
Last modified: Mon Mar 30 16:28:54 1998