NTSB F-16 & Cessna 150 midair preliminary report

http://www.ntsb.gov/_layouts/ntsb.av...15FA259A&rpt=p

On 7/18/2015 8:40 PM, son_of_flubber wrote:
http://www.ntsb.gov/_layouts/ntsb.av...15FA259A&rpt=p

To me, this is the crucial passage:
"At 1100:49, the radar target of the F-16 was located 1/2 nautical mile
northeast of the Cessna, at an indicated altitude of 1,500 feet, and was
on an approximate track of 215 degrees. At that time, the Cessna
reported an indicated altitude of 1,400 feet, and was established on an
approximate track of 110 degrees. At 1100:52 the controller advised the
F-16 pilot, "traffic passing below you 1,400 feet." "

I find transponder-reported altitudes to be pretty notoriously
inaccurate in general. So it seems to me that these two planes
indicating only 100 feet apart (but only reporting their altitudes in
100 feet increments) should have been considered at the SAME altitude.

With my PCAS, I consider +/- 400 to be the same altitude.

I was a bit stunned by the apparent lackadaisical behavior on the part
of both the F-16 pilot and the controller. Advice to turn should be
acted on immediately in a conflict situation. From the writeup it
seemed that neither the pilot nor the controller showed any concern
about such a close encounter. Of course that could simply be that the
printed word can't convey stress or tone in a voice.

Also notable is the fact that, had the F-16 pilot /_not_/ turned when he
did or /_had_/ turned when instructed, the collision would likely not
have occurred.

Vaughn, I agree with you on the PCAS altitude. My last conflict was
noted as -300 ft and, when I spotted the aircraft, it was about 100 ft
above my altitude.

On 7/19/2015 8:52 AM, Vaughn wrote:
On 7/18/2015 8:40 PM, son_of_flubber wrote:
http://www.ntsb.gov/_layouts/ntsb.av...15FA259A&rpt=p


To me, this is the crucial passage:
"At 1100:49, the radar target of the F-16 was located 1/2 nautical
mile northeast of the Cessna, at an indicated altitude of 1,500 feet,
and was on an approximate track of 215 degrees. At that time, the
Cessna reported an indicated altitude of 1,400 feet, and was
established on an approximate track of 110 degrees. At 1100:52 the
controller advised the F-16 pilot, "traffic passing below you 1,400
feet." "

I find transponder-reported altitudes to be pretty notoriously
inaccurate in general. So it seems to me that these two planes
indicating only 100 feet apart (but only reporting their altitudes in
100 feet increments) should have been considered at the SAME altitude.

With my PCAS, I consider +/- 400 to be the same altitude.

--
Dan Marotta

On Sunday, July 19, 2015 at 10:33:58 AM UTC-5, Dan Marotta wrote:

"At 1100:49, the radar target of the F-16 was located 1/2 nautical
mile northeast of the Cessna, at an indicated altitude of 1,500
feet, and was on an approximate track of 215 degrees. At that
time, the Cessna reported an indicated altitude of 1,400 feet, and
was established on an approximate track of 110 degrees. At 1100:52
the controller advised the F-16 pilot, "traffic passing below you
1,400 feet." "


So, the Cessna was pretty close to the beam, and therefore may not have shown up on the F-16s radar.

It almost sounds like both the controller and the Viper driver expected the other to take the appropriate action - neither took full responsibility for preventing the possible collision, expecting the other to do it!

So much for a transponder ALONE being the solution to midairs...

And until installing ADS-B Out in a certified airplane is a LOT cheaper, what are the chances that that Cessna owner would have bothered?

Would ADS-B in have provided timely warning to the Cessna of the approach of the F-16? As I understand it, since neither the Cessna or the F-16 had ADS-B out, the Cessna would not have received any traffic info from the ADS-B ground stations.

Thanks, FAA, for this idiotic implementation - withholding traffic data as an incentive to equip with ADS-B out!

Dual band ADS-B receivers SHOULD receive both weather AND all traffic! That would probably guarantee that just about everything flying would at least get traffic info!

Kirk
66

A note about transponder altitude inaccuracy. I also noticed significant inaccuracy when I used the Zaon MRX but once I switched to PowerFlarm I found mode C reported altitudes much more accurate, so I suspect the significant inaccuracy that Dan noted is due to MRX error, not necessarily transponder error.

Ramy

Ramy wrote:
A note about transponder altitude inaccuracy. I also noticed significant
inaccuracy when I used the Zaon MRX but once I switched to PowerFlarm I
found mode C reported altitudes much more accurate, so I suspect the
significant inaccuracy that Dan noted is due to MRX error, not
necessarily transponder error.

Ramy

You may get larger MRX errors if the glider does not have a local
transponder (that is being interrogated and seen by the MRX)...if it does
the MRX will use the transponder's transmitted altitude instead of it's
internal pressure sensor--which can be affected by cockpit ventilation.
With the number of issues that I believe Ramy had with his MRX maybe it was
not properly identifying the local transponder.

That could be the case, however... The MRX PCAS uses an internal
barometric sensor in the absence of an own ship's transponder. I've
observed its startup and noted that it initially reports a transponder
code of 3707 or some other nonsense, after my transponder is turned on
and begun replying to interrogations, the PCAS with show a TX code of
1200 and, finally, 1202 to which my Trig is set to reply.

I don't know what the required Mode C/S accuracy is below FL180, but if
it's +/- 200 feet, then you could occasionally see a 400' error. That or
my PCAS lost lock with my Trig, or it's just sloppy. Next time I see an
aircraft on which I've received an alert, I'll check the PCAS for the
transponder code it's using for its calculations. If I gain some
insight, I'll report it here.

On 7/19/2015 11:43 AM, Ramy wrote:
A note about transponder altitude inaccuracy. I also noticed significant inaccuracy when I used the Zaon MRX but once I switched to PowerFlarm I found mode C reported altitudes much more accurate, so I suspect the significant inaccuracy that Dan noted is due to MRX error, not necessarily transponder error.

Ramy

--
Dan Marotta

regarding altitude differences, 91.217 requires that the altimeter report pressure altitude correctly within 125 feet. So two aircraft, one reporting FL050 but 125ft high at 5,125 MSL and another reporting FL053, but 125ft low at 5,175 MSL will pass very close to each other, especially if one of them might be an ASH-30 in a level turn.

https://www.law.cornell.edu/cfr/text/14/91.217

On 7/22/2015 1:03 PM, Bob Pasker wrote:
regarding altitude differences, 91.217 requires that the altimeter report pressure
altitude correctly within 125 feet. So two aircraft, one reporting
FL050 but 125ft
high at 5,125 MSL and another reporting FL053, but 125ft low at 5,175
MSL will pass
very close to each other, especially if one of them might be an ASH-30
in a level turn.

https://www.law.cornell.edu/cfr/text/14/91.217


I believe the typical situation is much worse than that. 91.217 only
seems to require that the equipment meet that standard on the day it was
calibrated, and then 95% probability of meeting that standard is
accepted. After that, the equipment goes out to meet the real world
and all bets are off until the next calibration!

Also, remember that a transponder only reports altitude in 100 foot
increments, so 5,125 MSL might report the same as 5,199 MSL.