September 27, 2018
So about 5 or 6 years ago I wrote Xavion to back up all the cockpit displays I could think of on an iPad!
Backup attitude, GPS, speed, altitude, synthetic vision, weather, even hoops that would guide me to a power-off landing if the engine failed!
Well, I’ve been flying Xavion for quite a few years now, and I now have two cases where actual equipment failure caused me to use Xavion, and one case where I quickly coded Xavion to handle an un-expected occurrence in flight!
The most recent equipment failure was as follows:
I was at Pawleys Island, SC, at our little time-share house at the beach two days ago, enjoying the ocean but forced to come home thanks to Hurricane Florence, so I hopped into N844X (my Lancair) to come home. On climb-out, I noticed that my Garmin G900 was indicating ZERO AIRSPEED! DUH-OH! As well, my landing gear would not retract! It was obvious why: Because the indicated airspeed was zero, the landing gear system thought that I was on the ground and refused to retract as a safety measure! So now I had ZERO airspeed on my Garmin G900, but I still had to meet the requirement of staying below my gear-extended speed to avoid ripping the gear doors off!!!
How could I still honor airspeed limits without an airspeed indicator??
Well, of course I had Xavion running, and remember that Xavion estimates INDICATED airspeed by:
1: looking at the ground-speed from GPS,
2: subtracting out the winds as reported by ADS-B,
3: finding the standard air density by looking up the standard density based on GPS-altitude,
4: adjusting that standard density based on temperature and barometric pressure as reported by ADS-B,
5: with the exact true airspeed from (1) and (2) above, and the exact air density from (3) and (4) above, determines what the indicated airspeed MUST BE!!!
So Xavion shows AN ESTIMATED INDICATED AIRSPEED! THE PERFECT BACKUP FOR THE AIRSPEED INDICATOR IN YOUR AIRPLANE!
I’ve always found the Xavion indicated airspeed to be accurate to within about 5 knots, so when the airspeed on my Garmin G900 was showing ZERO, I just stayed below my gear-extended speed limits by looking at the airspeed on Xavion! Simple!!!!!
This allowed me to land with complete safety, use a little stick to get the mud dauber nest out of my pitot tube, curse myself for not doing a better pre-flight, and fly home comparing Xavion to my G900 and seeing that the results were nearly identical, which let me know that I really did get all the mud out of the pitot tube!
Anyhoo, a very very nice little use of Xavion there: Indicated airspeed without a pitot tube!
And earlier, a more dramatic test of the system:
A couple of years ago, I was at 27,000 feet, 275 knots, in solid IFR in a front, when suddenly the engine began… ‘popping’.
It was sort of a THOOMP, THOOMP, THOOMP, with the ITT and torque dropping a bit with each drop-out of power. Power was dropping.
You read about (and, if me, simulate) this type of thing all the time, but when it really is happening, it is a bit terrifying.
About the same time, the smell of jet exhaust started to become rather strong in the cockpit. Not enough to SEE, but I could really SMELL jet-exhaust in the cockpit.
I declared the emergency and started down.
The temperature in the cockpit was coming up during the descent as always, so I engaged the cabin intercooler to send cooler air into the cockpit.
WHOOOOSH! Out went the air from the cockpit and the plane de-pressurized instantly… I was now above 20,000 ft with no pressurization! I grabbed for my emergency backup oxygen mask always under my right hand and was never so happy to get down to 12,500 ft in my life.
The engine was now behaving normally again, and I landed.
I had Xavion running on my iPad for the entire event, so had at least a dozen or so airports ready for a power-off glide for the entire event if I needed them. Thanks to Xavion, my only fear was the pressurization loss and exhaust in the cockpit.. the partial engine failure was of less concern! This let me focus on dealing with my emergency oxygen system and talking to ATC, since I knew that Xavion was presenting me plenty of gliding options to nearby airports, continuously, throughout the entire event. When ATC advised me of the NEAREST airport, I was able to tell him, straight up, in the middle of the emergency, that I did not need the NEAREST airport… I needed the BEST airport, runway length and width considered! And, since I had Xavion, there was no problem at all seeing what airport that was! (Phoenix Goodyear in this case)
So Xavion worked perfectly.. it was awesome.
So, another very nice use of Xavion there: Power-off guidance to make it easy to set up an approach to the BEST airport around… the one with the longest and widest runway still in gliding distance!
(But what caused the engine surge, exhaust smell in the cockpit, and de-pressurization? A simple little hose had come loose! A little hose from the engine compressor to the intercooler that cools the pressurized air for the cabin. When that simple little hose came loose, the compressor of the engine, which is used to supplying small quantities of compressed air to the cabin, suddenly had ZERO back pressure on the pressurization system (the hose had come loose!) and was just dumping compressed air right back into the cowling. This caused the compressor surge, which kicked the engine exhaust back into the pressurization system… and into the cockpit. Thus the burned jet-fuel smell in the cockpit! Finally, when I engaged the intercooler: All the pressurized air in the cockpit went right out of the plane though the now-dis-connected hose. So one hose failure caused all those symptoms at once.
And, finally, the one that Xavion was NOT prepared for that I quickly CODED support for RIGHT after this event!
I was flying along at 16,500 in N844X coming out of a pretty major airport and an MD-80 sailed silently off my right side, opposite direction.
He was about a half mile away, maybe 500 feet above me, obviously inbound to the airport I had just left.
I enjoyed the silent view as he glided by and then got back to my usual scan.
About 2 minutes went by.
Then, suddenly: BANG!!!!
844X suddenly slammed be down into the seat with about 2 or 3 G’s of force, then slammed me up into the roof at negative G, then slammed me down into the seat again at 2 or 3 G’s.
Then continued as if nothing had happened.
It all happened in about ONE SECOND… NO POSSIBLE way to even think about reacting to it in any way at all.
I just sat there in the seat, amazed, my headset knocked into my lap, wondering if the plane was still structurally intact.
When the adrenaline wore off, I started to feel a steady aching in my neck from being thrown into the cockpit ceiling.
So here’s what happened: When I SAW the MD-80, he was drifting along harmlessly BESIDE ME (opposite direction).
BUT, unknown to me at the time, he must have CROSSED IN FRONT OF ME a few minutes earlier.
There was no way anyone could notice someone crossing their path while still several minutes ahead, so there is no way that I or anyone else could have seen this coming. The exact same thing would have happened to anyone. ATC never calls out that a plane has crossed the path that you will reach in several minutes.
Perhaps for this reason, wake turbulence is referred to as a ‘one-in-a-million’ event… but it isn’t.
I got hit hard with only about 2,500 hours of experience, and wake turbulence is not random. It is completely predictable.
And now Xavion shows it to you.
As I was thinking about that encounter the next day, my neck still aching form the impact, a way to track wake turbulence with an iPad dawned on me: Wake turbulence always emits from airplanes. And thanks to ADS-B, we know where the airplanes are. The next step is obvious.
So now, starting with Xavion 1.83, if you have an ADS-B receiver, then Xavion will, as always, track the location and altitude of all other airplanes.
But now: Every 10 seconds, each of those airplanes “lays a little wake turbulence egg”, simply depositing it into the sky.
Over the next 4 minutes, those little wake turbulence “eggs” will sink at the sink rate that wake turbulence is known to sink at, and as well move with the wind, as wake turbulence does. (the wind, as well, comes from the nearest ADS-B weather report)
Each wake turbulence “egg” is plotted as a little rotating cyclone, both on the MAP (with altitude difference from you displayed, just like traffic) and on the PFD, so you can clearly see it on your PFD.
As well, the COLOR of the wake turbulence eggs is handled exactly like the color of TRAFFIC icons, going from white to yellow to orange to red as it gets closer to you in separation and altitude.
After 4 minutes, each little wake-turbulence “egg” is dissipated, and disappears from Xavion.
So, when people talk about wake turbulence detection with doppler radar and complicated things like that, they seem to have forgotten the obvious: Wake turbulence is laid by airplanes, descends at a known descent rate, and drifts with the wind… and we know where the airplanes are, so tracking wake turbulence is actually shockingly easy” Just pop them out of the airplanes and move them with the laws of physics.
So why doesn’t EVERYONE do it??
Well, we have it now anyway!