Avionics News December 2015 - 21

commercial- and business-aircraft FMS once enabled to drive
autopilot functions.
Advances in both GPS navigation accuracy - brought by
the WAAS - and in digital cockpit systems slipped general
aviation operators' cockpit-control capabilities comparable
to FMS in business-turbine and commercial aircraft. And at a
fraction of the cost.

for more efficient climbs and descents from accounting for
aircraft weight and fuel use.
As use of FMS expanded, avionics makers added new
functions, among them automatic tuning of navigation radios,
graphical moving-map displays, fuel management, system
control and even in-flight datalink services.
Driving the birth of the modern FMS was an unanticipated
but significant change in the cockpit that came with the 757/767
pairing: the two-person cockpit.

FMS evolution: As in so many inventions,
in pursuit of improvement
It's all about brainpower
FMS evolved through random-area navigation computers to
elimiones referenced with inertial-navigation sensors and eventually
The reduction of crew to only pilot and first officer elimi
global-positioning satellites.
nated the traditional third crew member, the flight engineer
perBoeing took a new tack when it opted to merge the FMS and
or second officer. Boeing's 767 FMS predicted aircraft per
CDU into a single unit for the then-upcoming 767 wide-body
formance based on airframe and engine data in its memory
twin and its single-aisle cockpit cousin, the 757. Sperry, now
working with the real-time inputs from various systems on
Honeywell, first delivered this new
board - sensors such as an air data
sysFMS in 1982, and Boeing paired it with
computer and inertial reference sys
one of aviation's first - if not the first -
tem and RNAV.
precivil-aircraft glass cockpit.
The computed performance pre
TODAY, THE POOL OF
Boeing tapped the first FMS dede
dictions displaced more interpretive
FMS-LIKE PACKAGES
veloped from Sperry Flight Systems,
calculations made by the flight crew
which used VOR/DME-based RNAV
- data that proved relatively precise
perforthat appeared in the mid-1970s. An
based upon actual airplane perfor
RNAV navigator could store multiple
mance parameters, such as gross
VOR/DME pairs and compute aircraft
weight, speed, altitude, temperature
acposition from angle and distance, cross
and winds. In other words, more ac
referenced with the same data from
curate time and fuel predictions.
another station.
Without FMS or its abilities, navigation rested on the
With this freedom from flying VOR to VOR, the Federal
ground-based VOR and ADF backbones - systems that
Aviation Administration developed approach procedures to
worked well enough, but largely held flights to following
navigate over FMS waypoints. The efficiency improvement
zig-zag tracks across the landscape, increasing the time and
made RNAV highly appealing to the commercial carriers, and it
distance flown with a concomitant increase in fuel used.
But the advent of large memory banks and transistorized
was quickly adopted by airlines for terminal guidance.
computing processors, analog though it was, gave the FMS
General aviation operators soon after saw their own RNAV
computer the brainpower to perform the complex calculanavigators appearing as the technology was redesigned for the
tions needed to determine a precise position from the impresmaller aircraft.
cise analog navigation inputs.
Meanwhile, long-haul routes required other navigation
To work, the FMS needs both calculating capabilities and
methods; no VORs at sea. And when back over land, transitionplenty of memory for storing the position data of thousands
ing from long-range navigation to terminal navigation was a
of waypoints, airport runways, VOR and ADF stations.
problem, one complicated by the fact that in heavy aircraft, best
As FMS capabilities and brainpower increased, using the
airspeeds for climb and descent vary with the aircraft's weight.
FMS to guide the autopilot increased its appeal. The system
The solution emerged in that first Sperry FMS in the 757
consolidation continued, moving from alphanumeric keyand 767. It used microprocessor technology to compute
aircraft position from RNAV, inertial navigation system and
Continued on following page
other sensors; it also provided a rudimentary form of VNAV

CONTINUES
TO GROW.

AVIONICS NEWS

DECEMBER

2015

Table of Contents for the Digital Edition of Avionics News December 2015