Ingo Noka

Airspeed – Dead or Alive?

In Airmanship, Equipment, Gear, Knowledge, Ownership on May 19, 2013 at 4:47 pm

As they saying goes: it only takes two things to fly – airspeed and money. However, while it is usually better not to think too hard about the money you spend on flying, it is a great thing to know your airspeed.

Recently, I found out what it takes to fly without knowing your airspeed. After take-off, the airspeed seemed to come alive very late and be stuck at about 60 knots. By the time I decided that something is wrong with my airspeed indicator, I was already airborne and not enough runway left to abort the take off. I figured it is safer to fly as planned and use power, attitude, ground speed and eyeballs to fly at a safe speed. It turned out to be rather easy to achieve a straight and level flight without airspeed. After all, what speed can you possibly fly at with a 70% power setting without climbing or descending? The real question was, how would I achieve a reasonable approach speed and probably for the first time in my flying career I actually listened to ATC telling me wind speed and direction in their landing clearance.

As it turned out, landing pretty much uses all my brain’s processing power and I couldn’t for the life of me figure out what it means for my airspeed if I have a 60 knots ground speed and quartering 7 knots wind. I played it safe and thought that with a 70 knots ground speed I couldn’t possible be slower than 60 knots and a stall was surely not imminent.

To figure out what was wrong, the technicians opened up a lot of covers and even took out the stormscope to have a look at the tubes going onto the airspeed indicator. Everything seemed to be ok and the pitot tube wasn’t blocked (we thought).

Behind the instrument panel

However, blowing carefully against the ram air hole of the pitot tube is no way to check whether there is any blockage. The ram air produces surprisingly little pressure, so you will likely produce more pressure than necessary and the airspeed indicator will show speed all the way to maximum.

We all thought that the problem was solved and I did a test circuit – again without airspeed. Finally we decided to open up everything and we found the reason for the low airspeed indication – some sort of insect was building a nest in the pitot tube. We removed plenty of earth-like crumbs from the pitot tube, which looked like it belonged to a newly build house of a termite.

The remains of an insect nest from my plane’s pitot tube

I can tell you, that I never before was so relived when the airspeed came alive even during taxi and the airspeed indication was spot on (compared to ground speed on a calm day).

The moral of this story is – cover your pitot tube, even if you are on the ground only for a short time, be prepared to abort take off if airspeed does not come alive as usual and don’t be afraid to fly the aircraft with an airspeed indication. You should land as soon as you can, but if you follow your usual power and attitude settings, your airspeed will likely be in safe limits.

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