Detection of pitot tube and static port blockages

[NickN]

I had a question from a friend last night that I can't answer. What procedures are in place to detect pitot tube and static port blockages prior to departure of aircraft in high risk areas? For example if the aircraft overnights in a port where there is high insect movement etc.

[Daniel M]

nil (or minimal) airspeed increase on initial takeoff run...

[NickN]

I was thinking more along the lines of before the aircraft is trying to become airborne.

[Mick F]

Pitot tubes are left covered, however the static vents aren't covered.

The only means of detection pre-flight is to look in the tube with the naked eye. The next mean's of detection, are as Daniel said, rolling down the runway and not noticing an increase in airspeed.

The static vents generally aren't a problem with gathering insects, as the holes are very small. In the time I have been flying, I have never had a blocked static vent as the result of an insect.

Mick

[NickN]

Say you start your take-off roll and one of the airspeed indicators is not moving will the crew reject a take-off or continue in the hope the problem will resolve itself? I assume that by continuing there will be some sort of alarm or warning? Or is it acceptable to only have one airspeed indicator working?

On that note I'd assume it would be dangerous having no second guage to cross-reference against.

[Michael Mak]

I'd say they will reject the take off. The results could be disastrous if they continue the take off and become airborne.

See this accident with Birgenair Flight 301. The cause was a blocked pitot tube and the crew continued the take off.

http://en.wikipedia.org/wiki/Birgenair_Flight_301

[NickN]

There was a recent one involving an Austreaus (sp?) 757 in which the crew encountered a high level stall due to a bug blocking a pitot tube resulting in incorrect instrument readings but miraculously managed to bring the aircraft under control and land successfully.

[Mick F]

Take off would be aborted until the problem is resolved.

However, should the problem not be noticed until too late, and the aircraft becomes airborne, then a return to land would be carried out.

All passenger carrying RPT aircraft are equipped with dual pitot tubes that run on seperate systems, so should one not work, then the other could be used to land the aircraft.

Should both fail, well there's an old saying which every pilot should know, "Power + attitude = performance".

In one of the aircraft I fly, it is equipped with an Angle of Attack indicator, so if both my ASI's failed, I could easily land the aircraft by reference to the AOA indicator.

Mick

[Robert Zweck]

Originally Posted by NickN

There was a recent one involving an Austreaus (sp?) 757 in which the crew encountered a high level stall due to a bug blocking a pitot tube resulting in incorrect instrument readings but miraculously managed to bring the aircraft under control and land successfully.

Wasn't there a B757 where they taped over the static vents while they washed it....then got airborne but managed to get it down safely again?

[Matt_L]

Please refrain from quoting the whole previous post in your post, it is not necessary, thank you - mod

2 incidents I can recall of this nature.

One I think you mean is AeroPeru 603 at Lima, where the cleaner/ground staff had accidentally taped over static vents as you say.

It crashed into ocean- flight was at night and speed indications and altitude were conflicting that pilots lost orientation
http://en.wikipedia.org/wiki/Aeroper%C3%BA_Flight_603

Other one was a German charter airline Birgen Air 757 in Puerto Plata http://en.wikipedia.org/wiki/Birgenair_Flight_301 which was worst 757 crash in terms of fatalities. Cause was an insect who had gotten into at least 1 of the pitot tubes (and caused a blockage) as the aircraft had not flown in 25 days.

Both are featured on air crash investigations.