Inflight Vacuum Pump Failure!!

[ProprAire]

I want to share an eventful flight back to Rochester earlier this week that made me thankful for all the emergency training I’ve had from CFIIs during my 900+ hrs of flying.  I was cleared from Manchester, NH via the MHT-5/Cambridge transition-UTC-direct KROC at 8000 feet.  Upon reaching CAM I noticed I was about 1/2 mile north of course, unusual for my Aspen PFD providing GPS steering to the Century IIb autopilot.  Seconds later the aircraft made an abrupt turn north rather than a slight heading change to the south toward UTC.  My non-pilot wife asked if that was me or the autopilot maneuvering as I cross checked the instruments to find the AH completely out of whack and the vacuum gauge pegged on zero.  I immediately disengaged the autopilot and corrected the heading.  Fortunately, I was between layers so there was little risk of an unusual attitude even if I didn’t have the Aspen.  I assessed the situation as a non-emergency because I had the electric turn coordinator and if that failed, a GPS 396 on the yoke that I could have put into Panel Mode if I somehow lost the Aspen.  I elected to continue the flight and safely landed in ROC 1.5 hours later.   

There are 3 key lessons learned from this flight:

1.    Recurring training gave me confidence in my ability to rapidly assess the situation and take immediate corrective action.  I take quarterly proficiency flights in spite of flying ~100 hrs a year since buying my Mooney in 2006.  The CFII who administered my IPC in May just happened to be at the FBO when I returned.  I told her about the incident and thanked her for making me work so hard during that ride!

2.    Good systems knowledge was also helpful in determining the source of the problem and making the decision on whether or not to declare the emergency.  I must admit, I thought the Aspen provided the attitude stabilization input to the A/P.  Being able to correlate the spinning AH to the wild ride we experiencing with the A/P quickly dispelled that notion.

3.    I’m really glad I chose to make the investment in the Aspen PFD and keep redundant systems like the GPS 396 at the ready.  Given the nature of the failure, the outcome could have been far more severe had I been in IMC without an upgraded panel.  I wish I'd invested in a pack of post-it notes in the flight bag to cover the spinning AH as it was a distraction.

Fly safe!

[jetdriven]

A yoke mounted 396 or any other hand held GPS is not going to provide nearly enough information to keep wings level.

I believe the C-IIB gets is attitude reference from the AI and not the Aspen, and if the AI dies, the autopilot will do a barrel roll unless it gets a 30 degree bank signal from the AI.  Systems knowledge is gold here, and I am glad you are good in that area.

[KSMooniac]

The "virtual panel" page on the 396 or 496 is certainly a useful emergency tool and has enough fidelity to keep the wings level, or at least provide another reference if the AI rolls over.

[aviatoreb]

Quote: KSMooniac

The "virtual panel" page on the 396 or 496 is certainly a useful emergency tool and has enough fidelity to keep the wings level, or at least provide another reference if the AI rolls over.

[KSMooniac]

My 496 is fast enough IMO, but I know it has a faster processor and screen refresh compared to a 396, so perhaps the 396 isn't quite as good?

I too have an electric AI with a battery backup, so I don't plan to use the 496 option but it is there in case of doomsday I suppose...

[Immelman]

Good job! On my last flight, I had my vacuum pressure start wavering, and lowering slightly over time. 500 hours on the pump. I ordered a new one today and will stay in VMC conditions until then.

[Clarence]

Weird that for all the wow factor in glass panels you still have to keep your old vacuum atitude gyro because the new glass can't drive the old autopilot.  I guess I'll keep my old Brittain running for awhile yet!  

[aviatoreb]

Quote: KSMooniac

My 496 is fast enough IMO, but I know it has a faster processor and screen refresh compared to a 396, so perhaps the 396 isn't quite as good?

I too have an electric AI with a battery backup, so I don't plan to use the 496 option but it is there in case of doomsday I suppose...

[Piloto]

Quote: aviatoreb

I used to have a 396 - now I have an Aera - so yes - last resort it is there for me too.

Has anyone here tried to fly by 396/496 artificial instruments only?

[ProprAire]

Quote: aviatoreb

[jetdriven]

that virtual turn coordinator is based on ground track and it infers roll rate on that.  I couldnt imagine betting my life on it anymore than a jug of water on the glareshield.

[ProprAire]

Any idea how much I'll be paying for the new vac pump and installation?

[jetdriven]

Dan, a '77 J takes a  211CC (reman) or a 215CC vacuum pump (new).   194$ and 288$ respectively from aircraft spruce.  Looking at it, looks like a 2-4 hour job.  

Good thing while you are in there is to check is your vacuum hoses throughout and add a CV1J4 vacuum filter to keep the dust out of your gyros.  We are doing that.

[ProprAire]

Thanks! That's a comparable description to what my mechanic discussed prior to dropping off the plane with him Saturday. He says he pays extra attention to clean out any graphite that may have come out of the pump when it died.

[KSMooniac]

The R&R of the pump is a PITA due to accessability issues with the bottom nuts... some of that famous "Mooneys are hard to work on" conventional wisdom that is actually true for a change!    I did a proactive replacement in my first year of ownership as the current pump had 900+ hours on it and I figured it had earned retirement.  It helps if you have the special RAPCO wrench and a lot of curse words.