Telex Airman 850, Customer Maintenance Manual

Airman 850

Maintenance | en

23

Bosch Security Systems LLC

Customer maintenance manual

09-2021 | V07 | F.01U.264.819

6.2

Operational test of the microphone and headphone

i

Notice!

This method is an alternative to 

Speaker validation and adjustment, page 23 and requires a

known-good headset and an intercom.

1.

Insert the microphone and headphone plugs of a known-good (a.k.a. Reference) headset
into the intercom jacks on the “Copilot” (a.k.a. Right) side.
Aviation intercom is preferred such as Sigtronics Spo-22 2P, Pilot Usa Pa-200T, etc.

2.

Wear the Reference headset and place its microphone (with windscreen attached)
roughly 6mm in front of mouth. Speak into the microphone while adjusting intercom’s
squelch control and Copilot’s volume switch until you can hear yourself (side tone) in
both ears with sufficient loudness and clarity.
Please make sure the front side of the microphone faces towards the mouth.

3.

Insert the microphone plug of the DUT headset into the intercom jack on the
“Pilot” (a.k.a. Left) side, and remove the Reference microphone plug from the intercom’s
“Copilot” side. Place DUT microphone (with windscreen attached) next to the Reference
microphone. Talk into the DUT microphone and compare its loudness and sound quality
against that of the Reference microphone perceived in the previous step.
For comparison purpose, it might be necessary to talk into the Reference microphone
again after reinserting its plug into the intercom jack on the “Copilot” side.

4.

If the DUT microphone yields comparable loudness and clarity to that of the Reference
microphone, remove the plugs of the Reference headset from the intercom.

5.

Wear the DUT headset and insert DUT’s headphone plug into the intercom jack on the
“Copilot” side. Talk into the DUT microphone and assess its loudness and sound quality.
If the outcome is comparable to that of step 3, then the DUT headphone is deemed
acceptable.
Please make sure the DUT microphone is still connected to the intercom jack on the
“Pilot” side during this test.

6.3

Speaker validation and adjustment

6.3.1

Speaker sensitivity and frequency response verification

i

Notice!

Headphone specifications are designed to comply with FAA TSO C57a, DO-214 & DO-160D.
The headphone has two (2) operations (ANR version only):
1 - Passive: power is turned off.
2 - Active: power is turned on.

All modes tested, unless noted otherwise.

Transducer type:

dynamic

Transducer impedance (at the earphone
plug):

See Receiver impedance by model table in
Specifications, page 29, for impedance
according to model.

Sensitivity:

(All Models) 90 dB SPL ±5 dB at 1 kHz, 1 mW
input to headset, at LOW volume control
setting. 1 mV based on input impedance of
headset being tested.