Section 4 Reversionary Modes
4-6
IDU-450 EFIS Software Version 8.0H (Rotorcraft)
1
st
Ed Nov 2018
4.1.4. GPS
Failure
GPS degrades or fails as a result of loss of satellite information or GPS
equipment failure. When SBAS provides the integrity, the EFIS issues a
loss of integrity (LOI) caution within two seconds, if the current horizontal
protection level (HPL) exceeds the horizontal alert level (HAL). LOI caution
appears when there is no integrity monitoring and disappears when it is
restored.
Figure 4-2: LOI Caution
Further GPS degradation causes the EFIS to lose GPS updating of aircraft
position, ground speed, and ground track, and the ability to calculate the
wind information.
1)
(Loss of Integrity) displayed with no time delay.
2) HPL > HAL for the phase of flight currently in. Position is still presented
based upon a GPS navigation solution.
3)
(Loss of Navigation) displayed with no time
delay of the onset of the following:
a) The absence of power;
b) Equipment malfunction or failure;
c) The presence of a condition lasting five seconds or more where
there are an inadequate number of satellites to compute position
solution;
d) Fault detects a position failure that cannot be excluded within time-
to-alert when integrity is provided by FDE;
e) HPL > HAL on the final approach segment: Genesys Aerosystems
EFIS does not transition to DR navigation at this stage. A GPS
navigation solution is still presented; and
f) Where HPL > HAL on the final approach segment, this position
may still be satisfactory for GPS navigation. For example, an HPL
of 0.31NM exists, which means as soon as a transition to terminal
mode occurs, all alerts disappear. This is significantly important
during a wind change if the system had been in a DR mode.