Aircraft microphone is hot and picks up cockpit sounds when intercom is used.

Attributes
ACN	221543
Time
Date	199209
Day	Fri
Place
Locale Reference	airport : toa
State Reference	CA
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	tower : toa
Operator	general aviation : instructional
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Fixed Gear
Flight Phase	ground : preflight ground : holding ground other : taxi
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : single pilot instruction : instructor
Qualification	pilot : flight engineer pilot : atp pilot : cfi
Experience	flight time last 90 days : 30 flight time total : 4600
ASRS Report	221543
Person 2
Affiliation	Other
Function	instruction : trainee
Qualification	pilot : private
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	other flight crewa
Resolutory Action	none taken : unable other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

I've noticed that if using an intercom, with an auxiliary jack in the cockpit, the microphone supplied with the aircraft must be disconnected or else it will pick up random cockpit noise, blanketing any transmissions. Perhaps warnings should be incorporated into the aircraft manual or placarded in the airplane. Callback conversation with reporter revealed the following: reporter named the commercial intercom used. He thinks it is FAA approved. He is not sure if the fault lies with the intercom or with the aircraft's microphone which remains 'hot' whenever the intercom is keyed by vox, voice sounds. There is no evidence that this will result in a 'stuck microphone' but it can't help communications, either between pilots or between aircraft and ATC.

Original NASA ASRS Text

Title: ACFT MICROPHONE IS HOT AND PICKS UP COCKPIT SOUNDS WHEN INTERCOM IS USED.

Narrative: I'VE NOTICED THAT IF USING AN INTERCOM, WITH AN AUX JACK IN THE COCKPIT, THE MIKE SUPPLIED WITH THE ACFT MUST BE DISCONNECTED OR ELSE IT WILL PICK UP RANDOM COCKPIT NOISE, BLANKETING ANY TRANSMISSIONS. PERHAPS WARNINGS SHOULD BE INCORPORATED INTO THE ACFT MANUAL OR PLACARDED IN THE AIRPLANE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR NAMED THE COMMERCIAL INTERCOM USED. HE THINKS IT IS FAA APPROVED. HE IS NOT SURE IF THE FAULT LIES WITH THE INTERCOM OR WITH THE ACFT'S MICROPHONE WHICH REMAINS 'HOT' WHENEVER THE INTERCOM IS KEYED BY VOX, VOICE SOUNDS. THERE IS NO EVIDENCE THAT THIS WILL RESULT IN A 'STUCK MIKE' BUT IT CAN'T HELP COMS, EITHER BTWN PLTS OR BTWN ACFT AND ATC.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.