E135 triggers MSAW warning when the flight crew misunderstands altitude clearance.

Attributes
ACN	739972
Time
Date	200705
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : tyr.airport
State Reference	TX
Altitude	msl bound lower : 1500 msl bound upper : 2500
Environment
Flight Conditions	VMC
Weather Elements	other
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ggg.tracon
Operator	common carrier : air carrier
Make Model Name	EMB ERJ 145 ER&LR
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
ASRS Report	739972
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance other spatial deviation
Independent Detector	atc equipment : msaw other controllera
Resolutory Action	controller : issued alert controller : issued new clearance flight crew : returned to assigned altitude
Supplementary
Problem Areas	Flight Crew Human Performance Weather ATC Human Performance
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation

Narrative:

We failed to question an altitude clearance that seemed incorrect. While flying our WX radar malfunctioned. We contacted dispatch and they said that there was no WX in the area. After joining the arrival; ATC began vectoring aircraft around buildups. We decided to divert to tyr. During the descent; we were given radar vectors for the VOR DME runway 4 approach. We both thought that longview cleared us down to 1500 ft; and we descended to 1500 ft. We were in VMC and could plainly see the ground. While briefing the approach; I mentioned that the initial altitude was 2000 ft and we decided that it was allowed by ATC to be vectored at that altitude. ATC called back and said that he had a low altitude alert on us and to climb to 2500 ft and we did. ATC said that we were at the wrong altitude. Complied with new or correct ATC clearance. Try and be more careful.

Original NASA ASRS Text

Title: E135 TRIGGERS MSAW WARNING WHEN THE FLT CREW MISUNDERSTANDS ALT CLRNC.

Narrative: WE FAILED TO QUESTION AN ALT CLRNC THAT SEEMED INCORRECT. WHILE FLYING OUR WX RADAR MALFUNCTIONED. WE CONTACTED DISPATCH AND THEY SAID THAT THERE WAS NO WX IN THE AREA. AFTER JOINING THE ARR; ATC BEGAN VECTORING ACFT AROUND BUILDUPS. WE DECIDED TO DIVERT TO TYR. DURING THE DSCNT; WE WERE GIVEN RADAR VECTORS FOR THE VOR DME RWY 4 APCH. WE BOTH THOUGHT THAT LONGVIEW CLRED US DOWN TO 1500 FT; AND WE DSNDED TO 1500 FT. WE WERE IN VMC AND COULD PLAINLY SEE THE GND. WHILE BRIEFING THE APCH; I MENTIONED THAT THE INITIAL ALT WAS 2000 FT AND WE DECIDED THAT IT WAS ALLOWED BY ATC TO BE VECTORED AT THAT ALT. ATC CALLED BACK AND SAID THAT HE HAD A LOW ALT ALERT ON US AND TO CLB TO 2500 FT AND WE DID. ATC SAID THAT WE WERE AT THE WRONG ALT. COMPLIED WITH NEW OR CORRECT ATC CLRNC. TRY AND BE MORE CAREFUL.

Data retrieved from NASA's ASRS site as of January 2009 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.