C560XL pilot reported GPS malfunction that caused the aircraft to pitch down violently on the approa...

Attributes
ACN	1607869
Time
Date	201901
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	Marginal
Aircraft 1
Make Model Name	Citation Excel (C560XL)
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	GPS & Other Satellite Navigation
Person 1
Function	Pilot Flying
Qualification	Flight Crew Instrument Flight Crew Multiengine
Events
Anomaly	Aircraft Equipment Problem Less Severe Conflict Airborne Conflict Inflight Event / Encounter Unstabilized Approach Inflight Event / Encounter Weather / Turbulence

Narrative:

While downwind on approach to xxl; GPS failed and approach reported that radio was garbled and scratchy; after I called and reported loss of my primary navigational aids. I continued turning my #2 radio then the GPS (garmin 430) came back on line. As I started the approach needles swayed back and forth then settled down. Glide slope needle centered on glide path and after a few a few seconds needle and aircraft nosed down violently at 3000 fpm. I grabbed the controls and abandoned the approach. Approach asked if I needed assistance. I stated that I had navigational problems but wanted to try again. During 2nd approach I slowed aircraft too early from 170kts as requested; because needles were less erratic; but trailing traffic was closing on me and tower told me to abandon the approach. On 3rd attempt I flew the approach manually and maintained centerline averaging the heading because localizer needle and flight director swayed left and right.

Original NASA ASRS Text

Title: C560XL pilot reported GPS malfunction that caused the aircraft to pitch down violently on the approach.

Narrative: While downwind on approach to XXL; GPS failed and Approach reported that radio was garbled and scratchy; after I called and reported loss of my primary navigational aids. I continued turning my #2 radio then the GPS (Garmin 430) came back on line. As I started the approach needles swayed back and forth then settled down. Glide slope needle centered on glide path and after a few a few seconds needle and aircraft nosed down violently at 3000 fpm. I grabbed the controls and abandoned the approach. Approach asked if I needed assistance. I stated that I had navigational problems but wanted to try again. During 2nd approach I slowed aircraft too early from 170kts as requested; because needles were less erratic; but trailing traffic was closing on me and tower told me to abandon the approach. On 3rd attempt I flew the approach manually and maintained centerline averaging the heading because localizer needle and flight director swayed left and right.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.