A B757-200 pitched over at 1;800 ft on takeoff after the right autopilot was engage with LNAV and RN...

Attributes
ACN	877588
Time
Date	201003
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Initial Climb
Route In Use	SID ZZZ
Flight Plan	IFR
Component
Aircraft Component	Autopilot
Person 1
Function	Pilot Flying First Officer
Events
Anomaly	Aircraft Equipment Problem Critical Inflight Event / Encounter Loss Of Aircraft Control

Narrative:

Takeoff appeared normal to the flaps up selection. LNAV; VNAV; and right autopilot were engaged. At 1800 ft aircraft started to pitch down abruptly. 'Autopilot' EICAS warning light was on. Disconnected autopilot and began a 20-30 pound pull to arrest sink rate. Egpws warnings commenced at approximately 1500 ft. Aircraft bottomed out at 1100 ft; 240 KTS; clean configuration. It felt like runway nose down trim. After recovery; passing 4000 ft on departure; center autopilot was selected and all appeared normal thereafter. This could have been a very big deal at a little lower altitude. I watch the aircraft fairly carefully anyway and prefer to hand fly until medium altitude or higher. Needless to say; I will be even more attentive to RNAV; autopilot low altitude operations.

Original NASA ASRS Text

Title: A B757-200 pitched over at 1;800 FT on takeoff after the right autopilot was engage with LNAV and RNAV active. The First Officer disconnected the autopilot and with 20-30 pounds of force stopped the descent at 1;100 FT with EGPWS warnings active.

Narrative: Takeoff appeared normal to the flaps up selection. LNAV; VNAV; and right autopilot were engaged. At 1800 FT aircraft started to pitch down abruptly. 'AUTOPILOT' EICAS warning light was on. Disconnected autopilot and began a 20-30 pound pull to arrest sink rate. EGPWS warnings commenced at approximately 1500 FT. Aircraft bottomed out at 1100 FT; 240 KTS; clean configuration. It felt like runway nose down trim. After recovery; passing 4000 FT on departure; CTR autopilot was selected and all appeared normal thereafter. This could have been a very big deal at a little lower altitude. I watch the aircraft fairly carefully anyway and prefer to hand fly until medium altitude or higher. Needless to say; I will be even more attentive to RNAV; autopilot low altitude operations.

Data retrieved from NASA's ASRS site as of April 2012 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 B757-200 pitched over at 1;800 ft on takeoff after the right autopilot was engage with LNAV and RNAV active. The first officer disconnected the autopilot and with 20-30 pounds of force stopped the descent at 1;100 ft with egpws warnings active.