GA small aircraft apparent overshoot of altitude on climb. Transponder mode C no output.

Attributes
ACN	89943
Time
Date	198806
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : sna
State Reference	CA
Altitude	msl bound lower : 2000 msl bound upper : 2400
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : sna artcc : zoob
Operator	common carrier : air taxi
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	climbout : intermediate altitude
Route In Use	departure other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 153 flight time total : 23000 flight time type : 17
ASRS Report	89943
Person 2
Affiliation	government : faa
Function	controller : departure
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 153 flight time total : 23000 flight time type : 17
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	aircraft : equipment problem dissipated controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

When departing sna the climb portion of the IFR clearance was given as, 'maintain 3000', expect 6000' 10 mins later.' at takeoff the tower advised that my clearance was amended to 'maintain 2000', expect 6000' 10 later.' after takeoff and reporting to coast departure climbing through 600' coast replied with, 'not reading your transponder.' I immediately recycled the transponder, both through the code and activity modes. The immediate readout then was 2400' with an altimeter readout of 1400'. The transponder altitude of 2400' was reported with an immediate coast instruction to climb to 3000'. It is felt that last minute amendments to a clearance, especially during the initial takeoff or any other critical phase of flight, is definitely not a safe procedure. In this particular instance resetting the altitude alert system, the transponder and acknowledging these requests was an additional burden on the pilot. All this, along with the recycling of the transponder altitude indication and subsequent erroneous altitude callout by the pilot. Although in this case there was no involvement of altitude violation, other aircraft or safety of flight, the overall situation in another instance could have been serious. I would highly recommend not issuing amendments to a clearance when a pilot is involved in any critical phase of a flight, and especially not during takeoff. In this instance the change in altitude could just as easily have been issued by coast departure upon initial contact with them after takeoff.

Original NASA ASRS Text

Title: GA SMA APPARENT OVERSHOOT OF ALT ON CLIMB. TRANSPONDER MODE C NO OUTPUT.

Narrative: WHEN DEPARTING SNA THE CLB PORTION OF THE IFR CLRNC WAS GIVEN AS, 'MAINTAIN 3000', EXPECT 6000' 10 MINS LATER.' AT TKOF THE TWR ADVISED THAT MY CLRNC WAS AMENDED TO 'MAINTAIN 2000', EXPECT 6000' 10 LATER.' AFTER TKOF AND RPTING TO COAST DEP CLBING THROUGH 600' COAST REPLIED WITH, 'NOT READING YOUR TRANSPONDER.' I IMMEDIATELY RECYCLED THE TRANSPONDER, BOTH THROUGH THE CODE AND ACTIVITY MODES. THE IMMEDIATE READOUT THEN WAS 2400' WITH AN ALTIMETER READOUT OF 1400'. THE TRANSPONDER ALT OF 2400' WAS RPTED WITH AN IMMEDIATE COAST INSTRUCTION TO CLB TO 3000'. IT IS FELT THAT LAST MINUTE AMENDMENTS TO A CLRNC, ESPECIALLY DURING THE INITIAL TKOF OR ANY OTHER CRITICAL PHASE OF FLT, IS DEFINITELY NOT A SAFE PROC. IN THIS PARTICULAR INSTANCE RESETTING THE ALT ALERT SYS, THE TRANSPONDER AND ACKNOWLEDGING THESE REQUESTS WAS AN ADDITIONAL BURDEN ON THE PLT. ALL THIS, ALONG WITH THE RECYCLING OF THE TRANSPONDER ALT INDICATION AND SUBSEQUENT ERRONEOUS ALT CALLOUT BY THE PLT. ALTHOUGH IN THIS CASE THERE WAS NO INVOLVEMENT OF ALT VIOLATION, OTHER ACFT OR SAFETY OF FLT, THE OVERALL SITUATION IN ANOTHER INSTANCE COULD HAVE BEEN SERIOUS. I WOULD HIGHLY RECOMMEND NOT ISSUING AMENDMENTS TO A CLRNC WHEN A PLT IS INVOLVED IN ANY CRITICAL PHASE OF A FLT, AND ESPECIALLY NOT DURING TKOF. IN THIS INSTANCE THE CHANGE IN ALT COULD JUST AS EASILY HAVE BEEN ISSUED BY COAST DEP UPON INITIAL CONTACT WITH THEM AFTER TKOF.

Data retrieved from NASA's ASRS site as of August 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.