EAA - Experimental Aircraft Association  

Infinite Menus, Copyright 2006, OpenCube Inc. All Rights Reserved.



Tools:   Bookmark and Share Font Size: default Font Size: medium Font Size: large

Bits and Pieces Home | Articles | Polls | Issues | Subscribe

Bits and Pieces

What Would You Have Done With Complete Loss of Pitot Static?

By Ian Brown, Editor - Bits and Pieces, EAA 657159

In the middle of our warm dry summer I took off one day with my usual “let her fly off” technique, and everything looked normal until I looked to check my altitude and airspeed. Neither my Dynon EFIS nor my analogue gauges were reporting airspeed, and my altitude was stuck at the airport elevation. I immediately set engine, flaps, and trim for what I would do normally: full engine power, retract flaps, turn crosswind, and trim for modest climb. I made the radio call on initial climb, guessing at altitude, and noted that all gauges needing pitot static for reference were dead, including my transponder.

Van’s RV-9A, like other models, has two pitot static ports, connected by a length of 1/8-inch tubing, so instead of knowing that one is blocked, you don’t really know you have a problem unless both are blocked. The principle is that by having a port on each side you receive better balance; if there is wind pressure on one side of the fuselage, it’s likely that there would be a vacuum on the other. The two ports are made with pulled rivets with the centre shaft removed and are connected by a 1/8-inch tube with a T-connector going forward to the instrument panel. The actual diameter of the port entry is the size of the shaft of a pop rivet and is visually inspected for blockage on my walk-around.

Getting back to the exciting ride, I leveled out in the downwind, reported the difficulty to the traffic, and completed the circuit uneventfully. My approach was intentionally a bit hot. We have 5,000 feet of runway, so I planned to bleed off speed over the runway instead of risking a stall on final.

Interestingly, as I touched down, all gauges began to function normally. As I rolled I regained airspeed readout. Maybe my next action could be debated, but I decided to take off again, partly as a diagnostic and partly because I seemed to be able to handle the circuit with the inputs as described. As soon as I began to climb, the gauges failed again. Once more round the circuit and then wisdom took over from inquisitiveness. I landed safely, and obviously the next item on the agenda was investigating the static ports and their tubing. The ports themselves were clean as a whistle, with no signs of foreign material nearby. Access to the rear fuselage is gained by removing the panels separating it from the baggage compartment. There are about 20 screws. The reach to unscrew them is uncomfortable, so it’s not an area that gets a visual check other than at the annual.

The photograph shows the cause of the problem. The culprit has yet to be identified, but it’s probably some tiny spider mite. On removing the tubing I found both the longer starboard and the shorter port tubes completely blocked with a series of blobs of an orange waxy substance.

As luck would have it, there was no blockage in the longer tubing going forward, so the problem was resolved by removing the shorter aft sections and cleaning them.

Note to self: Thoroughly check the pitot static tubing at every opportunity, and block external access to the ports when the aircraft is not in use.

On looking back, I recall seeing tiny red mites climbing up the tiedown at the tail. I guess they had to be going somewhere. I’ve since made “remove before flight” flagged push pins for the static ports. If you have suggestions or comments, please don’t hesitate to share them below.

---------------------------

 
Copyright © 2014 EAA Advertise With EAA :: About EAA :: History :: Job Openings :: Annual Report :: Contact Us :: Disclaimer/Privacy :: Site Map