A GLF4 pilot encountered turbulence which led to the autoplt turning off and an altitude loss of 150...

Attributes
ACN	592811
Time
Date	200309
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : rsw.vortac
State Reference	FL
Altitude	msl single value : 45000
Environment
Flight Conditions	Mixed
Weather Elements	Thunderstorm Turbulence
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zma.artcc
Operator	general aviation : corporate
Make Model Name	Gulfstream IV
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 60 flight time total : 5600 flight time type : 800
ASRS Report	592811
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude inflight encounter : weather inflight encounter : turbulence non adherence : far non adherence : clearance other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : regained aircraft control
Supplementary
Problem Areas	Weather Flight Crew Human Performance Environmental Factor Aircraft
Primary Problem	Weather

Narrative:

On vector to avoid overflying cumulo nimbus build-up associated with tropical depression/storm at FL450, isa deviation went from +5 degrees to +34 degrees within a few mi. At isa greater than +20, autothrottles computer (performance computer) quit and autothrottles disengaged with loss of target EPR. Cruise mach dropped abruptly from .77 mach to .69 mach. FGS disengaged and shaker activated. Aircraft lost approximately 1500 ft in associated turbulence. Immediately requested and got block altitude FL430-FL450. Within 2 mins, exited area of hot air and returned to FL450. Called flight watch and made PIREP.

Original NASA ASRS Text

Title: A GLF4 PLT ENCOUNTERED TURB WHICH LED TO THE AUTOPLT TURNING OFF AND AN ALT LOSS OF 1500 FT.

Narrative: ON VECTOR TO AVOID OVERFLYING CUMULO NIMBUS BUILD-UP ASSOCIATED WITH TROPICAL DEPRESSION/STORM AT FL450, ISA DEV WENT FROM +5 DEGS TO +34 DEGS WITHIN A FEW MI. AT ISA GREATER THAN +20, AUTOTHROTTLES COMPUTER (PERFORMANCE COMPUTER) QUIT AND AUTOTHROTTLES DISENGAGED WITH LOSS OF TARGET EPR. CRUISE MACH DROPPED ABRUPTLY FROM .77 MACH TO .69 MACH. FGS DISENGAGED AND SHAKER ACTIVATED. ACFT LOST APPROX 1500 FT IN ASSOCIATED TURB. IMMEDIATELY REQUESTED AND GOT BLOCK ALT FL430-FL450. WITHIN 2 MINS, EXITED AREA OF HOT AIR AND RETURNED TO FL450. CALLED FLT WATCH AND MADE PIREP.

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 GLF4 pilot encountered turbulence which led to the autoplt turning off and an altitude loss of 1500 ft.