Monday, January 23, 2017

We interrupt this political rant to geek out about airplanes

I figure if I want to maintain the moral high ground with respect to my slogan, "Where nothing is off topic," I figure I should write about something other than politics now and again.  So here's an interesting bit o trivia about Air Force One.

You may have read in the news that Barack Obama's last flight aboard Air Force 1 had to divert from Palm Springs to March Air Force Base because of bad weather.  Actually, it wasn't Air Force One -- it's only called that if the president is on board, and at that point Obama was no longer president.  So the flight was called SAM44: Special Air Mission (or something like that) for the 44th president.  But it was the same aircraft that is used to transport the president.

But that's not the interesting part.

The interesting part is that PSP was reporting ceilings of 900 feet at the time SAM44 had to divert.  They had to divert because they were flying the VOR/GPS-B approach which has minimum around 2000 feet, not even close to being able to make it in with a 900 foot ceiling.  But there are two other approaches, the RNAV (RNP) Y RWY 31L approach and the RNAV (RNP) Z RWY 13R approach (which has one of the funkiest approach paths I have ever seen).  Both of these have minimums of 734 feet, well below the reported 900 foot ceiling.  Furthermore, the RNAV Z 13R approach would have aligned them with the prevailing winds at the time and allowed them to land straight in instead of circling.

So why didn't they fly that approach?

It's because the aircraft doesn't have the right kind of GPS.

Think about that: the airplane that carries the president of the United States is supposed to be chock-full of the latest super-secret military technology.  It's supposed to be able to survive a nuclear attack with enough capability remaining to issue the order for a counterattack.  But it can't land at Palm Springs if the ceiling is below 2000 feet because it lacks a GPS unit that you can put in a civilian plane for about $5000.

That's kind of mind boggling, but it turns out it's actually not so uncommon.  Retrofitting older airplanes with newer avionics is really hard, sometimes impossible.  Still, you'd think that for the president's plane they'd get it figured out somehow.


Duffy Fainer said...

Actually, just to put the "gps"gear in my single engine Grumman, would be closer to $20,000 installed.

How do you know what the avionics suite of the Boeing VC25 actually consists of?

Considering that the aircaft flies around the world non stop and lands in foreign countries, I suspect that it very much does not rely on foreign navigational aids for landing.

I would suspect that system was inoperative or unreliable at the time of the approach.

Ron said...

> How do you know what the avionics suite of the Boeing VC25 actually consists of?

Obviously I don't. All I know is that they were not able to fly an RNP approach. (OK, maybe they were able to but chose not to, but that seems very unlikely to me.)

Duffy Fainer said...

So, according to
"the aircraft incorporates state-of-the-art avionics and communications equipment with Stage III compliant engines."

I listened to the ATC recordings. Other business jets were also going missed, and diverting. I'm thinking that the conditions at PSP exceeded the minimums that SAM44 had for this particular mission despite the equipment onboard, and accounting for runway length and terrain. Why they were doing this while in the hold for the VOR-B approach? A longer run in from Thermal with more terrain clearance while waiting for higher ceilings.

There's a lot of terrain around that airport, and I'm sure all of that factored into the aeronautical decision making regarding diverting to March AFB and it's Ground Controlled Approach Controller, as well as the 13,300' runway