Figure 4-36 Gtp 59 Oat Probe Dimensions; Gtp 59 - Garmin GI 275 Installation Manual

4.6.2

GTP 59

An effective location for the GTP 59 OAT Probe is on or near an access panel on the bottom of the wing, or
in areas where it would mostly be shaded in straight and level flight.
For composite aircraft, the probe must be mounted on an access panel or inspection cover. A typical
installation example is shown in Figure 4-38. If the access panel or inspection cover is conductive, a non-
conductive doubler must be used and a minimum 0.5 inches of clearance maintained between the GTP 59
probe/terminal lug and any conductive element of aircraft structure. A typical installation example is
shown in Figure 4-39.
For metal and tube-and-fabric aircraft, electrical bond between GTP 59 and nearby aircraft metallic
structure must achieve a direct current (DC) resistance less than or equal to 2.5 mΩ with the connector
disconnected. It may be necessary to use a bonding strap to electrically bond the probe. Bonding strap
must:
1. Have the cross-sectional area greater than 0.016 square inches (approx 20,800 circular mils).
QQB575R30T437 7/16" tubular braid (24,120 circular mils) or QQB575F36T781 3/4" flat braid
(20,800 circular mils) meet this requirement.
2. Be as short as possible, not to exceed 6 inches. When installed, the strap must not loop back on
itself.
3. Use MS20659-130 lug and #10 stud (or larger) attached to local aircraft metallic structure with
minimum thickness of 0.032 inches.
4. Use a 5/16 stud size terminal lug connected directly to GTP 59 probe.
For metal and tube-and-fabric aircraft, if the GTP 59 is installed in an access panel in Lightning Zone 2A
(refer to Appendix G), the access panel must be at least 0.032-inch thick aluminum or, if the access panel
is less than 0.032-inch thick aluminum, a doubler that is at least 0.032-inch thick aluminum (per
Figure 4-37) must be installed.
For aircraft with metallic airframes, a doubler is required when the GTP 59 probe is installed in the skin.
The doubler must be a minimum of 2 inches and at least one gauge thicker than the skin with a minimum
doubler thickness of 0.032 inches. The doubler material and installation must be provisioned by the aircraft
structural repair manual or standard practices manual, or alternatively:
1. Use the same material as the aircraft skin. If the material used in the construction of the aircraft
skin is not known, 2024-T3 aluminum per AMS-QQ-A-250/5 can be used.
2. If corrosion protection methods are not specified by the model-specific aircraft standard practices
manual, the doubler material must be chemical conversion coated per MIL-DTL-5541 Type II or
MIL-DTL-81706 Type II and primed with a high-solids chemical and solvent resistant epoxy
primer per MIL-PRF-23377, Class N.
190-02246-10
Rev. 11

Figure 4-36 GTP 59 OAT Probe Dimensions

GI 275 Part 23 AML STC Installation Manual
Page 4-53