Home' RTCA Documents for Review : DO-253D_Change1_FRAC Contents 33
DO-253D Change 1
© 2019 RTCA, Inc.
126.96.36.199.2.1 Antenna Gain
Over the frequency range of 108.000 to 117.975 MHz, when the antenna under test is
terminated in 50 ohms and is mounted on a 4’ x 4’ (or larger) ground plane, the reception
of the vertically polarized component of a radiated signal in the horizontal plane shall
[LAAS-065] not be down more than 6 dB when compared to a standard vertically polarized
At any frequency within 108.000 to 117.975 MHz, the difference between the maximum
and the minimum reception of the vertically polarized component of radiated signals from
any directions in the horizontal plane shall [LAAS-066] not exceed 7 dB for Class A
receivers and shall not exceed Z dB for Class B receivers.
Each antenna manufacturer shall [LAAS-417] declare the minimum and maximum gain
including the effects of gain variation in the horizontal plane of the vertically polarized
188.8.131.52.2.2 Antenna VSWR
Over the frequency range of 108.000 to 117.975 MHz, when the antenna is mounted on a
4’ x 4’ (or larger) ground plane, the VSWR produced on the antenna transmission line by
the antenna shall [LAAS-067] not exceed 3:1.
Position and Navigation (PAN) Subsystem
The PAN equipment receives the LAAS messages that include differential corrections.
The differential corrections are added to the ranging measurements and used to compute a
highly accurate navigation solution with high integrity. The PAN equipment also receives
approach data from the LAAS messages and makes a selection based on the pilot’s request.
From this information, the PAN equipment computes guidance for the approach or the
guided takeoff that has been selected.
The hardware and software shall [LAAS-070] be designed and developed such that the
probability of providing misleading information and the probability of loss of function are
acceptable based on the system integrity and continuity requirements, respectively. This
requirement must be met when the equipment is in its installed configuration for the most
stringent operation supported. To demonstrate compliance, it will be necessary to conduct
a safety assessment to evaluate the system’s implementation against known failure
conditions. This safety assessment should be based upon the criteria of AC 23.1309-1()
for Part 23 aircraft, and AC 25.1309-1() for Part 25 aircraft, AC 27-1() for normal category
rotorcraft, and AC 29-2() for transport category rotorcraft.
Note: Failure conditions of GPS/LAAS that cause out-of-tolerance error conditions
during a CAT I approach, without identifying the data as invalid, may be classified
as hazardous/severe-major. Failure conditions of GPS/LAAS that cause out-of-
tolerance error conditions during a CAT III approach, without identifying the data
as invalid, may either be extremely improbable or not prevent a safe landing or
An acceptable means to demonstrate integrity compliance for PAN equipment is to show
that failures of the equipment that result in misleading information are not more probable
than half of the aircraft integrity requirement for the most stringent operation and aircraft
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