Piper PA30 twin commanche, caused a low altitude alert from approach control during a GPS approach. ...

Attributes
ACN	531180
Time
Date	200112
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : olv.airport
State Reference	MS
Altitude	msl single value : 1500
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : mem.tracon
Operator	general aviation : personal
Make Model Name	PA-30 Twin Comanche
Operating Under FAR Part	Part 91
Navigation In Use	other
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : atp pilot : cfi
Experience	flight time last 90 days : 40 flight time total : 15000 flight time type : 1500
ASRS Report	531180
Person 2
Affiliation	government : faa
Function	controller : approach
Events
Anomaly	non adherence : published procedure other spatial deviation
Independent Detector	atc equipment : msaw other controllera
Resolutory Action	controller : issued alert other
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance Airspace Structure
Primary Problem	Flight Crew Human Performance

Narrative:

Approaching olv on (NDB) or GPS approach runway 36, flying the GPS approach. Established inbound 2000 ft and passed 6 mi from ehago intersection, started descent to MDA 1080 ft. At approximately 1500 ft approach excitedly informed me of a low altitude alert and to stop descent immediately. I stopped descent until I was notified altitude alert stopped. Continued approach, broke out of clouds and canceled IFR, proceeded visually. In reviewing the commercial chart plate it shows descent from 2000 ft within 10 NM applicable and the profile view shows you should be level at minimums before ehago. This is what I was doing. Will there always be a low altitude alert when shooting the approach as published? An interesting observation: the commercial chart profile view depicts you should be level at minimums before ehago while compared to the government charts they do not depict this but a descent (constant) through ehago. Why the difference? Callback conversation with reporter revealed the following information: reporter stated that he had made this approach several times in the past and had never had a low altitude alert. He suggested that it might be because he was held high prior to approach clearance causing him to establish a higher rate of descent further out in the procedure turn limits. He was advised that the approach descent chart depictions are not to scale and are just a visual reference to make a non precision descent to the MDA prior to the airport.

Original NASA ASRS Text

Title: PIPER PA30 TWIN COMMANCHE, CAUSED A LOW ALT ALERT FROM APCH CTL DURING A GPS APCH. RPTR WONDERED IF EVERYONE WOULD RECEIVE AN ALERT AND WHY THE DIFFERENCE IN THE PROFILE DEPICTION OF THE APCH DSCNT BTWN THE COMMERCIAL AND THE NOAA APCH CHARTS.

Narrative: APCHING OLV ON (NDB) OR GPS APCH RWY 36, FLYING THE GPS APCH. ESTABLISHED INBOUND 2000 FT AND PASSED 6 MI FROM EHAGO INTXN, STARTED DSCNT TO MDA 1080 FT. AT APPROX 1500 FT APCH EXCITEDLY INFORMED ME OF A LOW ALT ALERT AND TO STOP DSCNT IMMEDIATELY. I STOPPED DSCNT UNTIL I WAS NOTIFIED ALT ALERT STOPPED. CONTINUED APCH, BROKE OUT OF CLOUDS AND CANCELED IFR, PROCEEDED VISUALLY. IN REVIEWING THE COMMERCIAL CHART PLATE IT SHOWS DSCNT FROM 2000 FT WITHIN 10 NM APPLICABLE AND THE PROFILE VIEW SHOWS YOU SHOULD BE LEVEL AT MINIMUMS BEFORE EHAGO. THIS IS WHAT I WAS DOING. WILL THERE ALWAYS BE A LOW ALT ALERT WHEN SHOOTING THE APCH AS PUBLISHED? AN INTERESTING OBSERVATION: THE COMMERCIAL CHART PROFILE VIEW DEPICTS YOU SHOULD BE LEVEL AT MINIMUMS BEFORE EHAGO WHILE COMPARED TO THE GOV CHARTS THEY DO NOT DEPICT THIS BUT A DSCNT (CONSTANT) THROUGH EHAGO. WHY THE DIFFERENCE? CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE HAD MADE THIS APCH SEVERAL TIMES IN THE PAST AND HAD NEVER HAD A LOW ALT ALERT. HE SUGGESTED THAT IT MIGHT BE BECAUSE HE WAS HELD HIGH PRIOR TO APCH CLRNC CAUSING HIM TO ESTABLISH A HIGHER RATE OF DSCNT FURTHER OUT IN THE PROC TURN LIMITS. HE WAS ADVISED THAT THE APCH DSCNT CHART DEPICTIONS ARE NOT TO SCALE AND ARE JUST A VISUAL REF TO MAKE A NON PRECISION DSCNT TO THE MDA PRIOR TO THE ARPT.

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.

Piper PA30 twin commanche, caused a low altitude alert from approach control during a GPS approach. Reporter wondered if everyone would receive an alert and why the difference in the profile depiction of the approach descent between the commercial and the NOAA approach charts.