**CDM Memorandum**

**Subject:** The Daily Download and Time-out Cancels

**To:** Daily Download Working Group

**From:** Rick Oiesen

**Date:** 18 April 1999

# Introduction

The purpose of the Daily Download, in brief, is to replace the OAG data
in the ETMS database with the air carrier's daily operational schedule,
which will presumably be more accurate than the OAG. There are three
types of inaccuracies in the OAG schedule that might be corrected by the
daily download.

1.  There might be flights in the OAG that are not in the daily
    operational schedule.

2.  There might be flights in the daily operational schedule that are
    not in the OAG.

3.  Flights that are in both the OAG and the daily operational schedule
    might have different data, e.g., different departure and arrival
    times.

At least three air carriers (AAL, AWE, and TWA) already send in a CDM
message for every flight in their daily operational schedule; this takes
care of the second and third inaccuracies; other carriers might well
adopt this practice also. This leaves the first inaccuracy, which leads
to erroneous flights being in the ETMS database, which ETMS eventually
time-out cancels. These flights cause demand to be over-predicted for
many hours and are therefore of great concern.

Our last discussion of the Daily Download left us wondering how many
time-out cancels there are with only OAG data. Knowing the magnitude of
this problem is important if we are to decide which of the alternatives
for dealing with it is best. This memo provides some data on this
question.

# The Data

Volpe gathered data on time-out cancels from February 17 through March
27. This data is summarized in Table 1. (An accompanying spreadsheet
titled TO_Cancels3_31_99.xls provides more detail in three ways. First,
it shows the data for each day. Second, it shows the data for all the
carriers that sent in CDM messages, not just the twelve primary
participating airlines. Third, it also includes data from February 9
through February 16 for selected carriers; this additional data is not
included in the summary statistics shown in Table 1.)

The five columns in Table 1 have the following interpretation.

-   *Air Carrier*: ID of the air carrier.

-   *Average number of OAG time-out cancels per day*: This is the number
    of flights for which ETMS had only OAG data (i.e., no flight plan or
    CDM message) and that did not fly.

-   *Average number of OAG time-out cancels per day per 1000 flights*:
    This normalizes the previous statistic to allow show the frequency
    of time-out cancels.

-   *Maximum number of OAG time-out cancels for a day*: The number of
    flights for which ETMS only had OAG data that were time-out
    cancelled show fluctuations from day to day; this column shows the
    worst case, i.e., the day with the largest number of time-out
    cancels.

-   *Average number of flights per day*: This number was not provided by
    our database and is just a quick visual estimate.

# Table 1: Statistics on Time-out Cancels for Major Carriers, February 17 Through March 27

+-------+--------------+---------------+--------------+---------------+
| # A   | **Average    | **Average     | **Maximum    | **Average     |
| ir Ca | Number of    | Number of OAG | Number of    | Number of     |
| rrier | OAG Time-out | Time-out      | OAG Time-out | Flights per   |
|       | Cancels per  | Cancels per   | Cancels on a | Day**         |
|       | Day**        | Day per 1000  | Day**        |               |
|       |              | Flights**     |              |               |
+-------+--------------+---------------+--------------+---------------+
|       |              |               |              |               |
+-------+--------------+---------------+--------------+---------------+
| AAL   | 3.0          | 1.4           | 39           | 2090          |
+-------+--------------+---------------+--------------+---------------+
| AWE   | 0.5          | 0.8           | 5            | 590           |
+-------+--------------+---------------+--------------+---------------+
| COA   | 0.3          | 0.2           | 3            | 1250          |
+-------+--------------+---------------+--------------+---------------+
| DAL   | 61.0         | 23.0          | 128          | 2650          |
+-------+--------------+---------------+--------------+---------------+
| FDX   | 33.9         | 56.5          | 59           | 600           |
+-------+--------------+---------------+--------------+---------------+
| GAA   | 0.5          | 1.5           | 3            | 300           |
+-------+--------------+---------------+--------------+---------------+
| MEP   | 0.3          | 2.0           | 2            | 140           |
+-------+--------------+---------------+--------------+---------------+
| NWA   | 1.6          | 1.0           | 8            | 1600          |
+-------+--------------+---------------+--------------+---------------+
| SWA   | 0.3          | 0.1           | 4            | 2500          |
+-------+--------------+---------------+--------------+---------------+
| TWA   | 0.0          | 0.0           | 1            | 800           |
+-------+--------------+---------------+--------------+---------------+
| UAL   | 1.9          | 0.9           | 15           | 2200          |
+-------+--------------+---------------+--------------+---------------+
| USA   | 0.1          | 0.0           | 2            | 2150          |
+-------+--------------+---------------+--------------+---------------+
| TOTAL | 195.4        | 7.3           | 398          | 26,700        |
+-------+--------------+---------------+--------------+---------------+

Note: The TOTAL includes all carriers that sent in CDM messages, not
just the twelve shown in this table. Also, time-out cancellations of
flights for which ETMS has a flight plan or a CDM message is also a
problem, but this problem is not addressed in this memo.

# Interpretation of the Data

Study of Table 1 leads to several conclusions.

First, for most carriers, the number of time-out cancels for which ETMS
only had OAG data hovers around one per thousand flights. While not
perfect, to me this seems like very good accuracy.

Second, TWA, which sends in cancellations for all flights in its copy of
the OAG that are not flying, has an almost perfect record. It had only
one time-out cancel in this thirty-nine day period. Once again, hats off
to TWA for outstanding accuracy. USA was close behind with only three
time-out cancels in this period. This shows that near-perfection is
possible.

Third, FDX and DAL lag in accuracy. In addition, some of the
sub-carriers not shown in this table but shown in the accompanying
spreadsheet also lag. These carriers need to do better.

Fourth, there are significant fluctuations around the daily average.
This is seen most clearly in the accompanying spreadsheet, but it can be
glimpsed in Table 1 by seeing that the maximum number of time-out
cancels on a day is in many cases much larger than the average.
Therefore, even though the average might be quite small, there can still
be isolated days when the number of time-out cancels is significant.

# Implications for the Daily Download

I assume that those carriers with sub-par performance will work to bring
their feeds up to the standards that other carriers have already
demonstrated to be achievable. Given this, the picture that we see is
one where on most days the ETMS database does not suffer much from
time-out cancels of flights for which it has only OAG data, but there
are scattered days in which this is a problem. Therefore, we need is a
daily download that recognizes this pattern and deals with it.

Here are the conclusions that I personally have come to. We can discuss
these at the next telcon and see what others think.

**1. Each airline should send in a CDM message for each flight.** I
don't think it matters whether this is done all at once in the middle of
the night or for each flight individually, say, 15 hours before it
departs. This ensures that every flight that is flying is in the ETMS
database and that it has the appropriate departure and arrival times.

**2. We should abandon the idea of a carrier notifying Volpe when its
daily download is complete and Volpe then removing flights that were not
in the daily download.** We thought that this was needed when we thought
that OAG time-out cancels was a continuing and serious problem. Now,
however, we see that it is not a problem for most airlines on most days.
The problem with Volpe removing flights from the database is that if
there is some foul-up, Volpe could erroneously remove flights, and this
could seriously damage the accuracy of the ETMS database. In my view, we
should not take this risk since this problem is episodic and rare rather
than continuing and serious. At the last telcon we talked about ways to
minimize this problem; my current view is that all this complication
should be avoided by not even taking this risk.

**3. An air carrier should be able to request the data on its flights in
the ETMS database.** As I see it, a carrier would request from the ETMS
database the data on its flights, much as it now requests with a re-sync
message (CTALIST) the ETMS data about its controlled flights. The
carrier could then compare what is in the ETMS database with what is in
its database, and it could then send to ETMS whatever modify, cancel,
and create messages are needed to correct the ETMS database. This would
not only take care of the OAG time-out cancel problem, which is the
primary concern of this memo, but it would correct **all** inaccuracies
for scheduled flights in the ETMS database. Moreover, the air carrier
could repeat this once every, say, three hours, to prevent the ETMS and
air carrier databases from drifting apart.