1. 6894 · workshop in software design lecture 2 · september 14, 1998 · CTAS
write on board in advance: handouts, names, Hoare quote
do first 6 slides quickly
remember to leave time for students to fill in info sheet: 5m?
don't dwell on first abstraction slide
might not have time for last two abstraction slides

2. the arrival scheduling problem
a resource allocation problem
aircraft arriving at an airport need to be sequenced for landing
can’t let them land in same order as they arrive in terminal area
runway may not be available when they get there
faster aircraft would overtake slower ones
current manual solution
aircraft pass through ‘meter gates’ on border of terminal area
arrivals at meter gate are delayed, and aircraft may be reordered
currently, controllers use judgment & experience to make these decisions
an opportunity for automation
better scheduling can increase airport throughput and minimize delays
(but cannot be optimal because of unpredictable weather, etc)
reduce controller workload, and thus improve safety
1/17/2019 daniel jackson

3. what is CTAS? basics Center/TRACON Automation System
set of tools to help controllers manage air traffic flow at large airports
developed at NASA by Erzberger and colleagues
chosen in 1991 by FAA as future automation system for terminal area
technical innovations
algorithms for trajectory synthesis and runway allocation
user interface: “human-centered automation”
a suite of tools
TMA (Traffic Management Advisor)
provides advisories on sequencing incoming aircraft to controllers in Center
FAST (Final Approach Spacing Tool)
provides advisories on sequencing for landing to controllers in TRACON
DA (Descent Advisor), EDP (Expedite Departure Path), UPR (User Preferred Routing)
exploit CTAS’s trajectory info for analyzing arrival/departure paths
CAP (Collaborative Arrival Planning)
pass scheduling info to airlines to optimize planning at hubs
1/17/2019 daniel jackson

4. what TMA does (roughly)
from
rapidly changing info (seconds)
radar information giving aircraft positions and velocities
flight plan info received from host computers and entered by controllers
availability of runways
slowly changing info (hours)
weather data
very slowly changing info (weeks)
map of airspace
static info
characteristics of different kinds of aircraft
computes
suggested arrival times at meter gates for incoming aircraft so
CTAS’s function is to provide advisories
not safety-critical in a narrow technical sense
but obviously reliability is of paramount concern
CTAS especially useful during ‘rushes’
1/17/2019 daniel jackson

5. organization of TMA software
INPUT SOURCE MANAGER
COMMUNICATIONS MANAGER
USER INTERFACE (TGUI, PGUI)
ROUTE ANALYZER
DYNAMIC PLANNER
1/17/2019 daniel jackson

6. our project what Erzberger told me (June 98)
algorithmic components (eg, DP, RA/TS)
well understood
mostly reliable
concerned about two areas of software
TGUI, PGUI code
CM (communications manager)
CM a much harder problem because we’d need to learn domain
why i chose CM
a more interesting problem
large-scale engineering issues
more about software design, less about algorithms, GUIs, etc
CM is a vital component of TMA and FAST
CM shapes the entire CTAS system
1/17/2019 daniel jackson

7. CM (Communication Manager)
main functions
maintains ‘aircraft tree’ (database of aircraft states)
calls algorithmic components periodically to process entire tree
maintains GUIs, handles user requests
basic stats
all in C
connected only by sockets to other processes; no shared memory
about 70kloc (including headers)
but only about 20kloc of essential stuff
history of development
algorithmic components are focus of NASA research, startingin 1980’s
dynamic planner was designed with OMT, an OO method
route analyzer translated from Fortran
CM was first written in 1991; most of current code from
1/17/2019 daniel jackson

8. basic control loop of CM
cm_motif.c main_loop (every 300ms)
cm_sock_util.c select_active_sockets
ism_socket.c ism_socket_read
cm_read.c read_ra
update_aircraft.c ism_socket.c:ism_socket_check handle_weather_update find_and_send_fps (1) request_etas_for_new_fps (2) distribute_ac.c: distribute_aircaft_to_ras (3) update_active_aircraft
update_aircraft.c update_aircraft
cm_send.c (1) forward_flight_plan_add (2) send_request_for_flight_plan (3) handoff_aircraft_to_ra
1/17/2019 daniel jackson

9. project goals & structure
experiment with new technology
design notions & tools
evaluate: pitfalls & successes
invent refinements, new approaches
improve CTAS
help NASA/CSC improve design of CM
explain existing problems and propose solutions
uncover problems
a research project
be willing to adjust plans as we learn more
lots of cooperation, between teams too
can change goals to more exciting ones
1/17/2019 daniel jackson