YOU DIRTY “RAT”

Question:  What is the worst that can happen to a plane with hydraulic problems? What are common problems?

Anthony Hazzard, Marlboro, New York

Answer:  The worst thing that can happen is, if all hydraulics are lost, the pilots may have little to no control of the plane.  They may be forced to try and control the plane through the use of asymmetric thrust as was the case when United’s flight 232 lost all its hydraulics on a DC-10 on July 19th, 1989, due to a freak series of events (the plane was modified after that to prevent a repeat).  Asymmetric thrust simply means applying more power on one side than the other to steer the plane.  If you’re thinking it’s a tricky maneuver to land a plane in this fashion, it is—exceedingly so. 

Under normal circumstances, the loss of one hydraulic system is not catastrophic as there are multiple systems independent of each other, any one of which can control the plane, not to mention systems themselves are redundant. 

For instance, if hydraulics can't extend the landing gear, there is another method to get the gear down by letting it freefall and cranking it into place or using other, similar methods.

Some hydraulic systems are engine-driven, while others are electrically driven.  Some are color-coded (green, blue, yellow), some are numbered and some are labeled A, B, etc. to distinguish the various systems.  Each aircraft manufacturer establishes its own method of labeling various systems.

Some planes even have a small propeller that may be extended beneath the plane to power the hydraulics (and part of the electrical system if needed) in the event of a dire emergency.  This propeller is called a “RAT,” pronounced just the way you see it.  It stands for “Ram Air Turbine.”  Aircraft I’ve flown which have a RAT include the Airbus 319/320 as well as the B-777.

Hydraulics provide power from fluid under pressure.  Controls such as the rudder, slats, flaps, landing gear, etc.) may all be hydraulically powered, and more than one hydraulic system may control a single control or control surface.

For instance, I once lost my Blue hydraulic system on an Airbus 320 while flying from Las Vegas to Washington, D.C.’s Dulles Airport.  Frankly, if I hadn’t seen the loss on my gauges I probably wouldn’t have noticed some of my control surfaces were moving at half their normal speed.  They just seemed a little sluggish.

Other hydraulic losses may result in more severe problems.  Once, pulling into the gate at Madison, Wisconsin in a B-727, we lost our primary (A) hydraulic fluid, which spilled all over the ramp.  A mechanic had to be flown in to repair the problem.  This particular hydraulic problem sticks in my mind because the entire crew—three pilots and four flight attendants, were driven in a van to Green Bay, about 140 miles away,  to crew another plane.

Somewhere along the way we had a flat tire, and wound up standing around in a field in our uniforms.  An old farmer rumbled up to us in a beat-up red tractor and asked us what our uniforms were for.  When we told him, he scratched his head and said, “Funny, I didn’t know United Airlines flew into Beaver Dam (I think that was the name).”

It just struck us funny, and I remember standing around under the hot sun in our by-then not-so-spiffy uniforms laughing at the ridiculousness of this airline crew, standing in a field in Wisconsin with a flat tire on our van, going no place any time soon.