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MAINTENANCE MANUAL
TPL-100A Processor / Part No. 940-0530-001
Use or disclosure of information on this page is subject to the restrictions in the proprietary notice of this document.
(1) UF19 Messages
Military Mode S formats are needed to help:
Normal daily operations in civil airspace
Military training operations outside of high-density airspace
Stop all unprotected transmissions. 
There are situations in which military operations benefit from a military Mode S format. 
The benefit is to not disclose aircraft data to unauthorized users. In these cases, a data 
protected military Mode S up-link/down-link format helps military operations. 
The MILACAS-FR Mode S data link addresses the need for private communication. It 
supports transmission and reception of data between formation aircraft. The 
MILACAS-FR system transmits and receives position, velocity, flight commands and 
other information using the DF19 extended squitter. 
Range and bearing measurements are derived by actively interrogating aircraft. For 
hybrid/passive surveillance use, it is necessary to make sure extended squitter content 
is correct. If DF19s are used for military applications, it is necessary to make sure the 
DF19 content is correct. 
The use of UF0 can cause an ambiguity (since transponders reply to a UF0 with a 
DF0). Use UF19 insted of UF0 to eliminate ambiguity. For military applications, UF19 
transmissions trigger a DF19 response for validation. Each UF19 transmission has the 
Mode S address as the aircraft identifier which selectively interrogates the aircraft of 
interest.
For a variety of military operations, data security techniques are used to protect the 
data contained in the up-link/down-link (UF19/DF19) formats. It is not appropriate to 
use these techniques on standard formats dedicated for civil use. 
In the MILACAS-FR implementation, UF19 interrogation rates change and depend on 
the distance between aircraft. For close-in aircraft, interrogation rates are not above 2 
Hz. For aircraft at longer distances (approximately 5 nautical miles), average 
interrogation rates do not exceed 1 per second.
The UF19 transmissions have power levels set with an algorithm consistent with TCAS 
II DO-185A MOPS. Due to the distance between aircraft in formation, the minimum 
power used is lower than the minimum requirement defined in the MOPS. Power levels 
must be in the 10-50 Watt range to lower unwanted interference outside of the 
formation. UF19 interrogations are used in the interference limiting calculations.
Long interrogations are better than short interrogations. The use of long military Mode 
S formats gives an essential improvement over existing military modes. Because of the 
data-link capability of Mode S, a long Mode S reply format consists of 112 bits:
Eight bits identify the format within a Mode S message.
104 bits are available for the data content. 
 Data content is protected using data protection techniques.