Question:

When declaring an emergency for a hydraulic system failure, what type of issues should be under consideration by the ARFF crews standing by? Is there a way to pass on to ATCT/ARFF what your major concerns might be upon your arrival, for example, if you’ve lost flaps and land fast, are your main concerns overheated brakes, stopping distance or both? Is nose gear steering a major concern once rudder authority is lost? What do you want us to focus on?

Answer:

A singular or multiple hydraulic system failure on an aircraft can create a wide variety of problems and raises important issues for ARFF crews to consider.

Hydraulics on planes run important components such as flight controls (including flaps), landing gear retraction and extension, nose wheel steering, reverse thrust, and brakes.  The items they run are all critical and are normally supplied by at least two separate hydraulic systems.  These systems are engineered so that a single hydraulic system failure will not greatly affect the flying characteristics of the aircraft.  However, some of the less critical components may be supplied by just one hydraulic system such as nose wheel steering.

For example, the B-757 has three hydraulic systems but only the left system powers the nose wheel steering.  The B-767 has also has three hydraulic systems but only powers the nose wheel steering off the center system.  Not having nose wheel steering is not typically a problem for landing.  As the aircraft slows, on the landing roll out, the rudder becomes less effective leaving only differential braking between the two main gear for limited steering.  (Note: A good indication that a landing aircraft does not have nose wheel steering is if the main inboard gear doors are hanging down.)  Once stopped the aircraft will need to be towed off the runway.

Modern wide body, long haul, airliners have three independent and redundant hydraulic systems.  Most narrow body airliners, including regional jets, have two independent and less redundant hydraulic systems.

Single hydraulic system failure often leads to a partial flap landing resulting in a slightly higher landing speeds, a slightly longer landing distances, and potentially no nose wheel steering problems.

In a dual hydraulic system failure the redundancy of the systems is largely lost on aircraft with three hydraulic systems and completely lost on aircraft with only two hydraulic systems.  At best you will have an aircraft with restricted flight controls (difficult to control) , partial or no flaps (noticeably faster than normal landing speeds and longer landing roll), hot breaks (from the faster speeds) and most likely no nose wheel steering.

One of the most important questions you can ask ATC regarding an emergency aircraft with a hydraulic system failure is whether it has a single, dual.

In Summary:

Single hydraulic system failure will normally not create a significant problem and will most likely result in a normal landing with the possibility of no nose wheel steering.

Dual hydraulic system failure is a significant problem for all aircraft, with noticeably longer landing distances required and hot brakes.

The above is general information, each type of aircraft and hydraulic system  may present unique situations.

Over the years I have experienced a few single system hydraulic failures.  A big thank you goes out to ORD, DFW, MIA, and CAI ARFF’s!

Captain John

About the Author:

John McLoughlin has been a commercial pilot for over 30 years. He is currently a B-767 Captain with a B-787 type rating for a major U.S. airline. He also holds a position on the Airline Pilots Association (APA) Union Safety Committee. Both John and his father, Jack, also served as volunteer firefighters.