Technical Provisions for Mode S Services and Extended Squitter

DRAFT - Working Paper ASP TSGWP11-01 for review by the TSG during the meeting in June 2011 in Paris
Appendix A A-93
A.3.2.2.2.3.3 Relative altitude
The 5-bit relative altitude field shall contain the difference in altitude between the own-aircraft and the alert aircraft. A
non-linear encoding shall be used to minimize the number of bits required for this field. A special encoding value shall be
used to indicate that the alert aircraft has no reported altitude. By convention, a positive value in the relative altitude field
shall indicate that the alert aircraft is above the own-aircraft.
Relative altitude shall be given by:
where altitudes are indicated in feet.
The TIS encoding for relative altitude shall be:
Relative altitude = AltitudeAlert aircraft – AltitudeOwn-aircraft
Relative altitude value
(alt) Relative altitude (feet)
0 0 ≤ alt ≤ +100
1 +100 < alt ≤ +200
2 +200 < alt ≤ +300
3 +300 < alt ≤ +400
4 +400 < alt ≤ +500
5 +500 < alt ≤ +600
6 +600 < alt ≤ +700
7 +700 < alt ≤ +800
8 +800 < alt ≤ +900
9 +900 < alt ≤ +1 000
10 +1 000 < alt ≤ +1 500
11 +1 500 < alt ≤ +2 000
12 +2 000 < alt ≤ +2 500
13 +2 500 < alt ≤ +3 000
14 +3 000 < alt ≤ +3 500
15 +3 500 < alt
16 No reported altitude
17 –100 ≤ alt < 0
18 –200 ≤ alt < –100
19 –300 ≤ alt < –200
20 –400 ≤ alt < –300
21 –500 ≤ alt < –400
22 –600 ≤ alt < –500
23 –700 ≤ alt < –600
24 –800 ≤ alt < –700
25 –900 ≤ alt < –800
26 –1 000 ≤ alt < –900
27 –1 500 ≤ alt < –1 000
28 –2 000 ≤ alt < –1 500
29 –2 500 ≤ alt < –2 000
30 –3 000 ≤ alt < –2 500
31 alt < –3 000
Draft
DRAFT - Working Paper ASP TSGWP11-01 for review by the TSG during the meeting in June 2011 in Paris