Tue Jan 20, 2015 8:52 pm
#1345877
I am a relatively new PPL with only a few hours logged since passing my skill test. I decided to fly on a clear cold winter’s day. The weather looked good, very little cloud, 10 km+ vis wind 4 kts down the runway. The only thing of note was an air temp of +3 and a dew point of +1.
I hadn’t flown since before Christmas and planned to just do a local bimble, with some general handling and maybe a few touch and goes on return. On checking the aeroplane (PA28), there was evidence of some light frost on the upper wing surfaces which was rapidly melting and easily brushed off with a gloved hand. The club has de-icing kit available, but I didn’t think I needed it, so didn’t take it outside with me.
After all the pre-flight checks, the engine started somewhat reluctantly – despite being primed and turned over by hand before engaging the starter. Once up and running I let it warm up gently and then called for taxi clearance (full ATC airfield). Taxyed to the holding point and carried out power checks without any problem. Got take off clearance and lined up on the runway and started the takeoff roll. Airspeed indicator showed acceleration as expected and I rotated at around 65 kts indicated. So far, so good.
As I climbed, I glanced down at the ASI which showed it dropping below 60 kts. I immediately lowered the nose and the speed gradually increased to just above 60 kts indicated. I checked the throttle was fully open and rpm was as expected, checked mixture was fully rich and carb heat was off. Still only showing above 60. Looking outside it was fairly obvious that the scenery was passing at more than 60 kts, so I continued the climb with about 5 degrees nose up. Something wasn’t quite right. Pitot heat! I had gone through the checklist during the power checks and the OAT was showing as +5, so I decided to leave the pitot heat off at before departure.
With pitot heat on, I continued with a shallow climbing turn and levelled off at circuit height. As I levelled out, the ASI showed just over 90 kts. That’s it, I thought, ice in the pitot tube. Won’t forget that one again! I thought about immediately returning, but the ASI was reading correctly now, probably just a bit of ice or moisture in the pitot tube. I continued a gentle climb to 2,100 ft. Time for some general handling. I started with a 180 to the left, then one to the right – quite happy not to lose any height in the turns. Next was a few stalls.
On climbing to my planned 3,300 ft, I noticed that the ASI immediately dropped below 60 kts again. Obviously attitude related. I decided that I couldn’t rely on the ASI. I needed to get back to base and land, but with an ASI I couldn’t rely on.
I decided to continue my climb and carry out a couple of stalls. I tried a clean power-off stall. Carb heat on, reduce the throttle to idle and keep some back pressure on the yoke, the ASI dropped as normal. The stall warner sounded and then the buffet before the full stall. Nose down, power on and recover. On lowering the nose, the ASI leapt to 120 kts. I wasn't doing anything like 120. It was obvious I was correct in assuming it was attitude related. Nose up under reads, nose down over reads, Straight and level unreliable.
Returning to base, there was no-one else in the circuit, so I asked for, and got, a left base join. I decided it was better to be high and fast than low and slow. There was a nice big runway, so I landed with a few knots more speed than I would have had with a working ASI, but there was enough runway to allow this.
I have decided to remain anonymous because I am sure that I will be slated by the sky gods on here for not returning immediately or for having an incompetent instructor who didn’t teach me to recognise speeds by listening (my instructor was excellent, incidentally). I don’t think that every eventuality can be covered on the PPL course. What my instructor did teach me was to remain calm, try to analyse the problem and work around it.
Was there anything I could or should have done differently?
After reporting the defect to the engineer, he said that it was probably fluid in the pitot tube.
I hadn’t flown since before Christmas and planned to just do a local bimble, with some general handling and maybe a few touch and goes on return. On checking the aeroplane (PA28), there was evidence of some light frost on the upper wing surfaces which was rapidly melting and easily brushed off with a gloved hand. The club has de-icing kit available, but I didn’t think I needed it, so didn’t take it outside with me.
After all the pre-flight checks, the engine started somewhat reluctantly – despite being primed and turned over by hand before engaging the starter. Once up and running I let it warm up gently and then called for taxi clearance (full ATC airfield). Taxyed to the holding point and carried out power checks without any problem. Got take off clearance and lined up on the runway and started the takeoff roll. Airspeed indicator showed acceleration as expected and I rotated at around 65 kts indicated. So far, so good.
As I climbed, I glanced down at the ASI which showed it dropping below 60 kts. I immediately lowered the nose and the speed gradually increased to just above 60 kts indicated. I checked the throttle was fully open and rpm was as expected, checked mixture was fully rich and carb heat was off. Still only showing above 60. Looking outside it was fairly obvious that the scenery was passing at more than 60 kts, so I continued the climb with about 5 degrees nose up. Something wasn’t quite right. Pitot heat! I had gone through the checklist during the power checks and the OAT was showing as +5, so I decided to leave the pitot heat off at before departure.
With pitot heat on, I continued with a shallow climbing turn and levelled off at circuit height. As I levelled out, the ASI showed just over 90 kts. That’s it, I thought, ice in the pitot tube. Won’t forget that one again! I thought about immediately returning, but the ASI was reading correctly now, probably just a bit of ice or moisture in the pitot tube. I continued a gentle climb to 2,100 ft. Time for some general handling. I started with a 180 to the left, then one to the right – quite happy not to lose any height in the turns. Next was a few stalls.
On climbing to my planned 3,300 ft, I noticed that the ASI immediately dropped below 60 kts again. Obviously attitude related. I decided that I couldn’t rely on the ASI. I needed to get back to base and land, but with an ASI I couldn’t rely on.
I decided to continue my climb and carry out a couple of stalls. I tried a clean power-off stall. Carb heat on, reduce the throttle to idle and keep some back pressure on the yoke, the ASI dropped as normal. The stall warner sounded and then the buffet before the full stall. Nose down, power on and recover. On lowering the nose, the ASI leapt to 120 kts. I wasn't doing anything like 120. It was obvious I was correct in assuming it was attitude related. Nose up under reads, nose down over reads, Straight and level unreliable.
Returning to base, there was no-one else in the circuit, so I asked for, and got, a left base join. I decided it was better to be high and fast than low and slow. There was a nice big runway, so I landed with a few knots more speed than I would have had with a working ASI, but there was enough runway to allow this.
I have decided to remain anonymous because I am sure that I will be slated by the sky gods on here for not returning immediately or for having an incompetent instructor who didn’t teach me to recognise speeds by listening (my instructor was excellent, incidentally). I don’t think that every eventuality can be covered on the PPL course. What my instructor did teach me was to remain calm, try to analyse the problem and work around it.
Was there anything I could or should have done differently?
After reporting the defect to the engineer, he said that it was probably fluid in the pitot tube.