A B737 crew intercepts the final approach course without clearance at yyz when they inadvertently le...

Attributes
ACN	528230
Time
Date	200110
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : cyyz.airport
State Reference	ON
Altitude	agl single value : 3000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-500
Flight Phase	descent : approach
Route In Use	approach : instrument non precision arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 240 flight time total : 14000 flight time type : 1400
ASRS Report	528230
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other spatial deviation
Resolutory Action	none taken : anomaly accepted
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

While being radar vectored to final approach course (localizer 24) and now two miles from intersection, we were on 132.8 (yyz approach control). I, the pilot not flying, mistakenly changed the active communication frequency to tower frequency in anticipation of the handoff. As soon as I started to change the frequency I realized what I did and quickly tried to find the original approach control frequency we were just using. After several attempts I just switched to tower, meanwhile the captain intercepted the final approach course with no approach control instruction to do so. On initial call to tower they cleared us for the approach and cleared us to land, all with no apparent regard to our self induced (approximately 45 second) lost communication situation. The reason this occurred was that there are two types of communication frequency heads used to transfer the 'standby' frequency to active frequency status. The older and less common types (the one we had) uses a toggle switch to activate the standby frequency to active frequency status. In the newer type, a button is pressed and it transfers the standby frequency which is always in the right window (of a two window frequency head) to the active frequency status, which is always in the left frequency window. The older toggle switch style communication also has a two window frequency head, but either window can be used as the active frequency or the standby frequency. I prefer the newer push button type communication head, it's less confusing.

Original NASA ASRS Text

Title: A B737 CREW INTERCEPTS THE FINAL APCH COURSE WITHOUT CLRNC AT YYZ WHEN THEY INADVERTENTLY LEAVE THE APCH CTL FREQUENCY WITHOUT A CLRNC. CONFUSION OVER THE OP OF THE RADIO CONTROL HEAD IS NOTED AS PART OF THE CAUSE.

Narrative: WHILE BEING RADAR VECTORED TO FINAL APCH COURSE (LOC 24) AND NOW TWO MILES FROM INTXN, WE WERE ON 132.8 (YYZ APCH CTL). I, THE PLT NOT FLYING, MISTAKENLY CHANGED THE ACTIVE COM FREQUENCY TO TWR FREQUENCY IN ANTICIPATION OF THE HANDOFF. AS SOON AS I STARTED TO CHANGE THE FREQ I REALIZED WHAT I DID AND QUICKLY TRIED TO FIND THE ORIGINAL APCH CTL FREQUENCY WE WERE JUST USING. AFTER SEVERAL ATTEMPTS I JUST SWITCHED TO TWR, MEANWHILE THE CAPT INTERCEPTED THE FINAL APCH COURSE WITH NO APCH CTL INSTRUCTION TO DO SO. ON INITIAL CALL TO TWR THEY CLRED US FOR THE APCH AND CLRED US TO LAND, ALL WITH NO APPARENT REGARD TO OUR SELF INDUCED (APPROX 45 SEC) LOST COM SIT. THE REASON THIS OCCURRED WAS THAT THERE ARE TWO TYPES OF COM FREQUENCY HEADS USED TO TRANSFER THE 'STANDBY' FREQUENCY TO ACTIVE FREQUENCY STATUS. THE OLDER AND LESS COMMON TYPES (THE ONE WE HAD) USES A TOGGLE SWITCH TO ACTIVATE THE STANDBY FREQUENCY TO ACTIVE FREQUENCY STATUS. IN THE NEWER TYPE, A BUTTON IS PRESSED AND IT TRANSFERS THE STANDBY FREQUENCY WHICH IS ALWAYS IN THE RIGHT WINDOW (OF A TWO WINDOW FREQUENCY HEAD) TO THE ACTIVE FREQUENCY STATUS, WHICH IS ALWAYS IN THE LEFT FREQUENCY WINDOW. THE OLDER TOGGLE SWITCH STYLE COM ALSO HAS A TWO WINDOW FREQ HEAD, BUT EITHER WINDOW CAN BE USED AS THE ACTIVE FREQUENCY OR THE STANDBY FREQUENCY. I PREFER THE NEWER PUSH BUTTON TYPE COM HEAD, IT'S LESS CONFUSING.

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.

A B737 crew intercepts the final approach course without clearance at yyz when they inadvertently leave the approach control frequency without a clearance. Confusion over the operation of the radio control head is noted as part of the cause.