Yes I was asking about the 4Y, just curious because I'm slightly surprised that the ASI over-read when you were still on the ground if the problem was that water was blocking the pitot static system, I mean normally if the static port was blocked or partially blocked then the ASI would continue to function usually with the static pressure that was trapped inside it, until of course when you started to climb and if sea level pressure remained trapped it would begin to under read.

And normally if the pitot tube was blocked then the ASI wouldn't move at all until you started to climb because it would simply be acting as an altimeter, if both were blocked I don't think much would move at all.

So I was wondering if you had any idea how your captain's ASI came to over-read?

When a static blockage occurs, it affects not just the altimeter and VSI, but also the airspeed indicator. If the static port blockage has happened on the ground, the air pressure that was ambient at the time the static became blocked is what ram air will be compared against during the takeoff. If lower pressure is trapped in the back end, or in other words, in the static end of the instrument, then the airspeed will read higher.

In this particular case, because of the combination of blockages and the way the system was plumbed, we didn't see uniform errors that immediately pointed to the entire system, or necessarily to the alternate static as a relief.

During the takeoff roll, normally the pilot not flying would set power, make airspeed calls, etc. The pilot flying might glance at the airspeed (which the captain did), but I didn't make any calls. I had been monitoring my airspeed, but last saw it much lower than the rotation speed. I was busy trying to do everything during the takeoff, including the fine setting of the propellers via the electric step-head motors (something not found on the original airplane, incidentally). When the captain called "Rotate!", it was then that I noted my airspeed was too low. My initial thought was that I'd failed to make the call. I hadn't. The captain rotated early, and with a nose-high attitude and considerably more drag, the airplane took a lot longer in the takeoff roll. It was when he realized that the airplane wasn't going flying, apparently the tail skid already having contacted the runway, that he abruptly brought the nose back down and got my full attention.

There was no way to reject the takeoff at that point. The airplane came with fairly weak, expander-tube brakes that would quickly fade with heat, and had no reverse. Dumping the retardant would have had the effect of coating the brakes and runway with slick retardant and making stopping impossible. Going was the only option, and we went, albeit with some confusion in indications and with the trees in our way. I think it was mostly the gear that went through the trees, rather than the whole airplane; no damage from the trees was observed.

The event underscores another principle that should be followed (but wasn't, that day); knowing where on the runway you can safely reject, and where you should be off the ground. A good habit, even (and especially) in light airplanes, is knowing the runway and having features or points along the runway in mind where you'll either reject if you're not off, or where you'll expect to be getting airborne. This serves as an additional safety tool.

I always made a habit in light airplanes of walking the runway before taking off, if I could. Obviously at a busy metro airport, this wasn't always possible. But at runways where the takeoff really would become critical, such as rough dirt or gravel or grass runways in tight canyons or other short field events, I always made a habit of pacing the runway off and inspecting it as I went. This would include making a note of where I expected to be airborne or where I could reject and get stopped. It might be as simple as noting it would by that pile of rocks or by this bush...but having a good concept of what to expect during the takeoff, and a way to measure the performance in addition to staring at the airspeed indicator, is always a good idea.

The airplane I'm flying presently uses up a great deal of the runway. In my original groundschool for this airplane, the instructor liked to say "If you don't like seeing red lights during the takeoff, you won't like flying here." I was used to seeing the red lights during the takeoff roll, so wasn't overly shocked at the frequency with which we are in them, and we do very much abide the takeoff speeds...but we're flying a "numbers" airplane. Many light airplanes are flown as much by feel as by numbers, and rightfully so. The 4Y, likewise, was flown by feel much of the time rather than by numbers, though we always respected the numbers...and as you can see, an early rotation had dire consequences in takeoff performance. A proper analysis at the time would have included the observation that although the airspeed was indicating high enough to rotate, perhaps the ground speed looked inadequate, and perhaps it as too soon on the runway.

The airplane in question was of WWII vintage, and had fairly limited performance charts. They were the original WWII charts, in fact, as was the flight manual, general and armament manual, mx manual, etc. With a recent frontal passage, a change in air pressure, and a headwind, and limited takeoff performance date beyond experience and some elementary calculations, the captain used his best judgment (which turn out to be that great, it would seem). He could be forgiven for seeing the airspeed rise more quickly than anticipated, given the headwind, and at the time, the altimeter difference seemed a fairly insignificant issue given the mission. My altimeter reflected field elevation when set to the altimeter setting, and the conversation was simple, along the lines of "yours is correct, we'll use yours."

This brings up another note, which is that we had dual altimeters; one for each side. Many light airplanes, especially single engine airplanes, have only one airspeed indicator, one altimeter and one VSI. Discrepancies may not be as easy to note. Thus it may be that the VSI that's off slightly may be the only initial indication of a bigger problem, or the altimeter that won't quite set right.

Another takeoff in an other place in the 4Y began normally, with all normal airspeed indications, but toward the latter part of the roll, as we rotated, the speed bled back and began to decrease. There was no stopping at that point, and we had a low overcast. As we entered it the speed finally bled back to zero in the climb. We flew pitch, and power. We attempted to correct with alternate static, but to no practical avail. This reaction is typical of a static blockage, where airspeed tends to bleed off as altitude increases. Once we were up and stable, rather than attempting to turn around in a mountainous area and go back and land, we got safe, and I went below and forward, where I was able to break static line connections and eventually restore instrumentation. This isn't something that's usually possible, or advisable, in a light airplane.

At the destination, we removed all the pitot and static line segments, as well as the pitots, and blew them all out into filters. We found water and several insects in various points, which had provided variable blockages. The blockages leaked air and weren't consistent, and didn't add up to an obvious cause as it was happening. That event illustrated the wisdom of not worrying too much about the "why" so much as simply flying the airplane.

;)

but I did read your account with interest.

The trouble is you should both have rejected the take off way before taking what could have proved a serious problem into the air.

The lesson is not about instrumentation but allowing a problem to unnecessarily develop which could have cost you your life, your crew their life and maybe many innocent people on the ground.

It is one thing pilots making a mistake in light aircraft but quite another when multi crew professionals make such an elementary mistake.

Hmm...so I guess what could have happened is that the pressure was low when it rained, the low pressure was trapped and then when you went flying the pressure was higher. I'm not an expert on pitot static systems but I would have thought it would have taken a huge pressure change throughout the day to cause the 25 knot difference in the instruments that you described in your description of the incident.

Rejecting the takeoff in those airplanes is nearly an impossibility, for some of the reasons I indicated. It is NOT like rejecting a takeoff in almost anything else.

Whether or not the takeoff should have been rejected is academic, given that it's no longer possible, and that it happened a long time ago. It involved a fairly egotistical vice president of the company as captain, and a brand new copilot who was making his second flight in the airplane (me) with a rapid dispatch enroute to a fire...for which we didn't even have the coordinates on takeoff.

You do have a knack for missing the point, and attempting to inject your understanding into things that you don't understand.

Rejecting the takeoff wasn't an issue. We were going to a fire. The airplane was loud enough that nearly all communications were done with hand signals. During the takeoff roll, one earcup in my headset failed, and I could barely hear. This failure wasn't actually discovered until later, but I don't hear communications well if it's just through one ear. The captain thought all was well, and rotated; I was heads-down as required to mainpulate the step head switches for that installation. Electric controls on hydromatic propellers usually required some manipulation on takeoff. Being my second flight, I was busy.

The captain made the rotation call, I checked my speed, yelled out that it was low, and continued setting the power. With many airplanes, the speed transitions through the rotation speed to takeoff safety speed fairly quickly, so it's not uncommon to check speed and check again to see it's made a substantial leap. As the speed was indeed rising, I made the callout that it was below rotation speed, and by the time I glanced up again to double check, he had already rotated. It wasn't a long runway.

As I said, this happened a number of years ago. Aerial fire is a very different kind of operation. We were firefighters first, and pilots a very close second. We were not moving an airliner, but a firetruck with wings, and dropping the load during a reject would have prevented a successful reject (again, for reasons previously cited). Keeping the load meant too much weight for the reject, and dropping it after rotation meant risking hitting people on the ground with 18,000 lbs of retardant. Much better to increase flap slightly maintain obstacle clearance, and go fight fire. Which is exactly what we did.

The example has been given here to augment a discussion of instrument errors. It appears to have been wasted on you.

It lit off surprisingly well, by eyewitness accounts. I wasn't aware of it until later when approached by a crash rescue specialist who commented on the fireball. His comment was that it encompassed the entire tail of the airpalne. When he first mentioned the fireball, I thought he was referring tot he fire we had just dropped on, not anything to do with our aircraft. I commented that we hadn't seen it, as we'd been involved with a smoke column and the drop. He wasn't talking about that at all, but the magnesium flash. Apparently the action of it being ground along the runway, along with steel bolts and the steel to which it was attached making sparks, it touched off quite nicely, and did a lot more damage than I'd have thought possible.

Grind that magnesium block into shavings or powder and burn it, instead. You'll get a hot class D fire that's blindingly intense.

I'm no expert on the dynamics of the system either. I do know what actually happened, and taking into account any possible instrument error or pitot error that may have been in the system to begin with, the contamination of the system, and the fact that a frontal passage had recently occurred, whatever combination of factors applied,they made for the situation as I've described it to you.

Tried that too.

I filled a cardboard box, about 6" cube, with magnesium cuttings from a turret mill. Actually I emptied the contents of a hoover which had been used to hoover up the swarf during milling. I then set fire to the box with a blowlamp, stepping back fairly quickly....

What happened?

Not a lot. The stuff burned very slowly.

The problem was obviously a lack of oxygen. To make magnesium particles go up fast, when packed tightly enough to ignite from each other, one needs to mix the stuff with an oxidiser of some sort.

Really.

There is another lesson there somewhere, but I suspect it will be equally lost.

Well actually it doesnt require oxygen to "burn".

I read chemistry in my first year, so had plenty of time to experiment with magnesium and a few other more exciting things. := You are right, chunks of the stuff do not "burn" all that "well"; I very much doubt this is what happened to our friend, but it makes for a good read.

Believe whatever you want. I was there. You were not. I'm not going to get sidetracked into another idiotic discussion about what you do and don't believe. Clearly the point was lost on you, and evidently you have more interest in chasing side stories and shooting down the discussion, than participation, so I'll leave it to you.

I didn't see the fireball. It was described to me by a crash rescue firefighter assigned to the temporary tanker base in Brooksville, Florida, at the time. It was significant enough that the National Interagency Fire Center sent several of their personnel, including the head of the aviation section and the head of the maintenance section, to see it personally and to discuss what had happened. We sat for three days during these discussions, then were released and sent back to Wyoming, where crews worked around the clock for several weeks reskinning and rebuilding the back end of the airplane, before we took it back out on fire contract again.

It's largely irrelevant to the point for which the example was used, which involved instrument errors. Again, that the point is lost on you isn't really my problem or concern. If you wish to discuss the point of the thread, which is instrument errors, and 91.213 with respect to legality, deactivation, placarding, replacement, etc...by all means do. The example used was ancillary to that discussion as an example only, and quite frankly I've no interest in playing your games. If you want to discuss the subject, by all means, do. Otherwise, take your shots and have your fun, because we're not going down that road again.

Yes but this is a discussion forum.

By all means give examples BUT as with any accident expect us to look beyond the immediate cause of the accident. The process leading to an accident usually starts well before the actual accident and the accident often doesnt happen for the most obvious reasons. In your example you blame the accident on the faulty ASI whereas I dont think that is the full story.

You see it differently, which is fine, that is why we debate the issue.

I think the problem should have stayed on the ground and you have given some reasons why it didnt. I agree some of those reasons may have been justified, others even understandable, because we have all made the mistake of being overtaken by the pressures of the situaution.

Dont take it personally. I have been blunt in the past with regards your colourful aviation career but your stories are interesting and raise some points that are worthy of discussion.

I haven't been reading the private flying section for long, am I missing some previous history?, how come a lot of threads end up with Fuji Abound and IO540 vs SNS3GUPPY, is this a long running thing?

No, not really, Mr Guppy is relatively new and has some interesting stories which are certainly way beyond my experience involving small arms fire, combat zones, aerial fire fighting etc. Some of the experiences he recounts and the views he expresses are thought provoking, add to the colour of the forum and are more interesting than other topics to debate. My interpretation of events is often different from his which adds to the debate.

Sorry if I am being a bore. Perhaps I should leave others to comment on the stories rather more than me but it is difficult not to debate points which just dont seem to add up unlike most posts on here.

I don't blame the faulty instrument in the least. It was pilot error, every step of the way, period, end of story. HOWEVER, analysis of that incident (not accident, and classed as an incident with potential by the investigating agency) is not why that incident was introduced. A full blown analysis of that event is fine, in another venue, but not appropriate to the discussion...which is why I didn't go into a lot more detail about what happened.

I could expand considerably on that event, but most of it isn't germane to light airplane operations. The only real part that is relevant in this case is the instrument issue, which is why it was introduced. The rest in this case makes for some interesting after-dinner conversation, but it's not a conversation for this thread.

I can't give you the dynamics or even a description of the ensuing magnesium fire, because I didn't see it. Like many who are involved in a situation, I would make the worst witness to the event, because I wasn't one. I was a participant, and can only follow what described to me by aircraft crash rescue specialists on scene (who were witnesses), and by an entire temporary tanker base staffed with career firefighters.

Insofar as instructive events, the instrument part is of far more interest than the peripheral moments, such as the tailskid strike. The matter was dealt with by a government investigative team, as well as handled and fixed in a full repair station. The entire event is more of a humorous story than a serious scary one, when the remainder of the story is factored in, and doesn't speak highly of the captain on that flight.

From the perspective of the junior crewmember on that trip, I can only say that we often come up through the ranks at any place or work or at any point in the industry, looking to those more senior than ourselves, and tend to make observations about what traits or characteristics we would like to emulate, and which we would like to forsake. Numerous points could be cited which were duly noted as not worthy of repetition in the future, and I would prefer to look back on that moment as a great learning experience.

The moment was best summed up later that summer when I was with another senior pilot in a company C-130. As we rolled down the runway, backtaxiing, he began to pull back on the control column repeatedly in a mock effort to raise the nose. He turned and looked at me, and asked "Why am I?" We both knew to whom he referred, and I couldn't have summed it up any better, myself.

WOW, a guy asks a simple question about a turn coordinator in a C172 and now we are talking about rejected takeoffs in two crew large aircraft and magnesium fires.........:rolleyes::bored:

The original poster PM'd me and we discussed the matter of the original post privately. Additional comments have arisen from thread drift. A certain amount of drift is acceptable, as any conversation, on the internet or spoken in person, will naturally take a course. Excess drift that takes away from the original point or diverges at such a wild angle, however, is probably best left for a different thread.

Hey
Sorry I went MIA since posting this threat, things got busy with work and personal life.

Thought I would mention, the Owner of the plane went flying the very next day and said the turn coordinator was fine! I thought I was going crazy. I flew it a few days later, and sure enough, I flipped the Master Switch, and it sounded just as I thought it did.

I have NO IDEA why the turn coordinator suddenly got so quiet I could not hear it, but it does work.... :*

Probably a good thing, My truck decided to not start the next day - had to have it towed to a shop and replace a crankshaft position sensor. Ironically costing the same amount as that flight would have cost. So maybe it was meant to be.

I suppose that if your truck had been equipped with a second attitude indiactor, you would not have needed the crankshaft position sensor...

I would say 'significant' rather than 'huge'. If you do the half rho vee squared for 70 and 95 knots (in metric) to get the dynamic pressure:

0.5 x 1.225 x 36 x 36 = 794 Pascals
0.5 x 1.225 x 49 x 49 = 1471 Pascals
The difference is 677 Pa, so about 7hPa, 7mB or about 0.2 in Hg.

If you say so.

I've seen altimeter changes of a thousand feet when crossing a front, and during a frontal passage; an inch drop is possible, so .2 inches isn't really all that much.

A five hundred foot indication difference with frontal passage is common.