Flight crew of a lear 25 lost assigned communications with center during high altitude climbing to c...

Attributes
ACN	374306
Time
Date	199707
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : sgf airport : mkc
State Reference	MO
Altitude	msl bound lower : 28000 msl bound upper : 36000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zkc
Operator	common carrier : air taxi
Make Model Name	Learjet 25
Operating Under FAR Part	Part 135
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 140 flight time total : 7600 flight time type : 3500
ASRS Report	374306
Person 2
Affiliation	company : air taxi
Function	flight crew : first officer
Qualification	other other : other pilot : instrument pilot : commercial
Experience	flight time last 90 days : 100 flight time total : 1350 flight time type : 100
ASRS Report	374300
Events
Anomaly	aircraft equipment problem : less severe other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : overcame equipment problem
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

During our departure out of stl to elp, we were cleared to climb to FL280. After leveling off at FL280, we were given a frequency change from 132.65 to 133.47. Unable to contact center we went back to the previous frequency of 132.65 and were unable to contact center either. Then we attempted to contact FSS and were unable to reach anyone there. Realizing this, we proceeded with the lost communication procedures, squawked 7600 and climbed to our efc of FL390 ten mins after departure. During the climb we continued to attempt to regain 2 way radio communication and was able to establish contact with a low altitude center frequency. That controller notified me to call center. When making that call I was told that ATC did not receive the 7600 transponder code until climbing out of 35600 ft. The probable cause of this event is that when changing from our assigned code of XXXX to 7600 there is a lag in reception from when the change is made to when ATC receives the new squawk code. This lag probably a function of the position of the radar in the sweep and the condition of both the radar and transponder. Another contributing factor can be the high climb rate of the learjet 25. I believe a procedure that may prevent this from occurring again is to squawk 7600 and wait 2-3 mins to give the radar and ATC enough time to receive and act on the aircraft's communication loss.

Original NASA ASRS Text

Title: FLC OF A LEAR 25 LOST ASSIGNED COMS WITH CTR DURING HIGH ALT CLBING TO CRUISE ALT, BUT SUBSEQUENTLY RE-ESTABLISHED COM USING A LOWER ALT FREQ.

Narrative: DURING OUR DEP OUT OF STL TO ELP, WE WERE CLRED TO CLB TO FL280. AFTER LEVELING OFF AT FL280, WE WERE GIVEN A FREQ CHANGE FROM 132.65 TO 133.47. UNABLE TO CONTACT CTR WE WENT BACK TO THE PREVIOUS FREQ OF 132.65 AND WERE UNABLE TO CONTACT CTR EITHER. THEN WE ATTEMPTED TO CONTACT FSS AND WERE UNABLE TO REACH ANYONE THERE. REALIZING THIS, WE PROCEEDED WITH THE LOST COM PROCS, SQUAWKED 7600 AND CLBED TO OUR EFC OF FL390 TEN MINS AFTER DEP. DURING THE CLB WE CONTINUED TO ATTEMPT TO REGAIN 2 WAY RADIO COM AND WAS ABLE TO ESTABLISH CONTACT WITH A LOW ALT CTR FREQ. THAT CTLR NOTIFIED ME TO CALL CTR. WHEN MAKING THAT CALL I WAS TOLD THAT ATC DID NOT RECEIVE THE 7600 XPONDER CODE UNTIL CLBING OUT OF 35600 FT. THE PROBABLE CAUSE OF THIS EVENT IS THAT WHEN CHANGING FROM OUR ASSIGNED CODE OF XXXX TO 7600 THERE IS A LAG IN RECEPTION FROM WHEN THE CHANGE IS MADE TO WHEN ATC RECEIVES THE NEW SQUAWK CODE. THIS LAG PROBABLY A FUNCTION OF THE POS OF THE RADAR IN THE SWEEP AND THE CONDITION OF BOTH THE RADAR AND XPONDER. ANOTHER CONTRIBUTING FACTOR CAN BE THE HIGH CLB RATE OF THE LEARJET 25. I BELIEVE A PROC THAT MAY PREVENT THIS FROM OCCURRING AGAIN IS TO SQUAWK 7600 AND WAIT 2-3 MINS TO GIVE THE RADAR AND ATC ENOUGH TIME TO RECEIVE AND ACT ON THE ACFT'S COM LOSS.

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.

Flight crew of a lear 25 lost assigned communications with center during high altitude climbing to cruise altitude, but subsequently re-established communication using a lower altitude frequency.