C421 pilots reported complete brake failure during taxi that resulted in a taxiway excursion.

Attributes
ACN	1454285
Time
Date	201705
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Golden Eagle 421
Operating Under FAR Part	Part 91
Flight Phase	Taxi
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	Normal Brake System
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Commercial Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 125 Flight Crew Total 6300 Flight Crew Type 300
Person 2
Function	Pilot Not Flying Captain
Qualification	Flight Crew Commercial Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 18 Flight Crew Total 2019 Flight Crew Type 80
Events
Anomaly	Aircraft Equipment Problem Less Severe Ground Excursion Taxiway

Narrative:

Before the plane was started; brakes and lines were inspected fully. Before start; brakes were applied and engine start was done with full brakes. When I first started taxiing the aircraft from the general aviation terminal; brakes were used to reposition the plane from parking to the taxiway effectively. [Later I] started applying brakes and noticed there was no brake pressure on either left or right brake. Did notice that the right engine low hydraulic pump light had come on. Engines were at idle. The plane veered to the right and the right main wheel left the taxiway surface. Tried using differential thrust from the right engine to raise the wheel back to the taxiway. The right main was not coming back to the taxiway surface. I kept the plane controlled using power as to not strike a propeller into a taxi light. Once clearing the propellers from striking a taxi light I tried again to bring the plane back to the taxi area using power from the right engine. The plane did make it back to the taxiway and the left main came onto the surface without an issue; still having no brakes. Once I realized there were still no brakes; I closed throttles; mixtures; and secured plane and then called the tower asking for assistance.

Original NASA ASRS Text

Title: C421 pilots reported complete brake failure during taxi that resulted in a taxiway excursion.

Narrative: Before the plane was started; brakes and lines were inspected fully. Before start; brakes were applied and engine start was done with full brakes. When I first started taxiing the aircraft from the general aviation terminal; brakes were used to reposition the plane from parking to the taxiway effectively. [Later I] started applying brakes and noticed there was no brake pressure on either left or right brake. Did notice that the right engine low hydraulic pump light had come on. Engines were at idle. The plane veered to the right and the right main wheel left the taxiway surface. Tried using differential thrust from the right engine to raise the wheel back to the taxiway. The right main was not coming back to the taxiway surface. I kept the plane controlled using power as to not strike a propeller into a taxi light. Once clearing the propellers from striking a taxi light I tried again to bring the plane back to the taxi area using power from the right engine. The plane did make it back to the taxiway and the left main came onto the surface without an issue; still having no brakes. Once I realized there were still no brakes; I closed throttles; mixtures; and secured plane and then called the Tower asking for assistance.

Data retrieved from NASA's ASRS site 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.