N162PQ

On December 24, 2017 about 1808 PST, SkyWest Airlines Flight 3567 (SKW3567), a Bombardier CRJ9, registration N162PQ, operated below the minimum vectoring altitude (MVA) while conducting an instrument approach to the Rogue Valley International – Medford Airport (MFR), Medford, Oregon and initiated a climb after receiving an alert from the Enhanced Ground Proximity Warning System (EGPWS.) The crew and passengers were not injured and there was no damage to the airplane. SKYW3567 was operating under the provisions of 14 Code of Federal Regulations (CFR) Part 121 as a scheduled passenger flight from Salt Lake City International Airport (SLC), Salt Lake City, Utah to MFR and instrument meteorological conditions prevailed at the time.

History of Flight

At 1801:45, the Seattle Air Route Traffic Control Center (ZSE) sector 10 controller responsible for SKW3567 contacted the Eugene (EUG) Medford approach controller sector controller and advised that SKW3567 was direct to the fix CEGAN and was requesting the VOR/DME-C (VHF Omni-directional Range/Distance Measuring Equipment) approach with the arc into MFR. The Medford sector controller responded "perfect" and the sector 10 controller transferred control of the flight to the Medford controller before it entered EUG airspace.

At 1802:09, the pilot of SKW3567 contacted the Medford sector controller and reported "we are at one two thousand direct to CEGAN for the V-O-R D-M-E charlie."

At 1802:18, the Medford sector responded "SKW3567 Cascade approach cross CEGAN at or above seven thousand eight hundred cleared V-O-R D-M-E charlie approach via the arc."

At 1802:28, the pilot of SKW3567 responded "alright ah cross CEGAN at or above seven thousand eight hundred and we are cleared for the V-O-R D-M-E ah charlie at ah thirty five sixty seven."

At about 1803:07 the flight crossed the initial approach fix CEGAN at a mode C reported altitude of 11,800 feet above mean sea level (msl) and joined the 27 DME arc off the Rouge Valley VORTAC (VHF Omni-directional Range/Tactical Air Navigation)..

At 1804:59, the mode C altitude information indicated the flight descended below 10,000 feet while still established on the 27 DME arc.

At 1806:12, SKW3567 entered an 8,700-foot MVA area at a mode C reported altitude of 8,300 feet.

At 1806:28, the Medford sector controller instructed the pilot of SKW3567 to contact the Medford tower controller on frequency 119.4 MHz at the fix GOLLD. The crew read back the instructions.

At about 1808:08, SKW3567 turned right and joined the final approach course at the fix BRKET. The mode C reported an altitude of 7,800 feet.

At 1808:20, the pilot of SKW3567 contacted the Medford sector controller and reported "just ah confirm we've ah show an obstacle on the ah approach at ah seventy two twenty nine." Five seconds later the pilot of SKW3567 reported in a climb for a GPWS alert. The Medford sector controller asked the pilot to "say again". The pilot responded, "we got a terrain warning we are climbing". The Medford sector controller asked the pilot to say intentions. The pilot of SKW3567 responded "climbing to eleven". There was no reply by the air traffic controller.

At 1809:31, the pilot of SKW3567 requested the instrument landing system (ILS) runway 14 approach into MFR. The Medford sector controller responded by issuing vectors for the approach.

At 1810:04, the pilot of SKW3567 transmitted "approach SkyWest thirty five sixty seven we received a ah G-P-S or a excuse me a G-P-W-S which is one of our terrain warnings ah that ah comes up when ah we are too low and we just wanted to let you when we called you we wanted to let you know that we thought were ah too low for this sector and we wanted to confirm with you the altitude on the approach". The Medford sector controller responded, "stand by".

At 1811:06, the Medford sector controller transmitted "SkyWest thirty five sixty seven what I'm showing on my approach plate is after CEGAN one zero thousand on the arc until you are ah established inbound is that what you are showing". The pilot responded, "that's what we show we were assigned an altitude of seven thousand eight hundred for SkyWest ah thirty five sixty seven". The Medford sector controller responded, "SkyWest thirty five sixty seven roger that altitude was ah at or above seven thousand eight hundred until established". The pilot of SKW3567 responded "and when we were established on the arc, we were ah we were established on a lower altitude than ah". A different SKW3567 pilot transmitted that they would discuss it on the ground via a telephone.

Radar Data

In general, two types of radar are used to provide position and track information for aircraft cruising at high altitudes between airport terminal airspaces, and for those operating at low altitude and speeds within terminal airspaces.

Air Route Surveillance Radars (ARSRs) are long range (250 nautical mile) radars used to track aircraft cruising between terminal airspaces. ARSR antennas rotate at 5 to 6 rotations per minute (rpm), resulting in a radar return every 10 to 12 seconds; there is no weather data associated with the radar return. Airport Surveillance Radars (ASRs) are short range (60 nautical mile) radars used to provide air traffic control services in terminal areas. ASR antennas rotate at 13 to 14 rpm, resulting in a radar return every 4.6 to 5 seconds. The ASR can detect precipitation and display it in six levels of precipitation on the controller's display or the tower display workstation (TDW). The weather data is updated every 60 seconds.

A radar detects the position of an object by broadcasting an electronic signal that is reflected by the object and returned to the radar antenna. These reflected signals are called primary returns. Knowing the speed of the radar signal and the time interval between when the signal was broadcast and when it was returned, the distance, or range, from the radar antenna to the reflecting object can be determined. Knowing the direction that the radar antenna was pointing when the signal was broadcast, the direction (or bearing, or azimuth) from the radar to the object can be determined. Range and azimuth from the radar to the object define the object's position.

To improve the consistency and reliability of radar returns, aircraft are equipped with transponders that sense beacon interrogator signals broadcast from radar sites, and in turn broadcast a response signal. Even if the radar site is unable to sense a weak reflected primary return, it will sense the response signal broadcast by the transponder and be able to determine the aircraft position. The response signal can also contain additional information, such as the identifying "beacon code" for the aircraft, and the aircraft's pressure altitude (also called "Mode C" altitude). Transponder signals received by the radar site are called secondary returns. SKW3567 was assigned a beacon code of 6040.

Radar data for this report was obtained from the Federal Aviation Administration (FAA) EUG ASR. The EUG plot playback (PPB) data was useable, of good quality, and was part of the STARS. Figure 1 illustrates the flight track of SKW3567 as the aircraft flew the VOR/DME-C instrument procedure into MFR. Figure 2 illustrates the location of SKW3567 as it descended below the 10,000-foot procedure altitude. Figure 3 illustrates the position of SKW3567 when the crew began their climb in response to the GPWS warning.

Figure 1 - Flight track of SKW3567 as the aircraft flew the VOR/DME-C instrument procedure into MFR.

Figure 2 - The location of SKW3567 as it descended below the 10,000-foot procedure altitude.

Figure 3 - The position of SKW3567 when the crew began climbing the aircraft.

Weather Information

Airport weather observations for MFR were obtained from the National Weather Service. Airport weather information found in the Meteorological Aerodrome Report (METAR) for MFR originated from an Automated Surface Observing System (ASOS). The following METARs were issued for MFR for the time period surrounding the incident:

[1753 PST] METAR KMFR 250053Z 15004KT 10SM BKN 064 OVC090 06/03 A3015 RMK AO2 SLP218 T00560028=

[1853 PST] METAR KMFR 250153Z 0000KT 10SM OVC070 06/03 A3017 RMK AO2 SLP223 T00610028=

MFR Instrument Procedure

MFR was served by 9 instrument approach procedures, one of which was the VOR/DME-C. According to the FAA, an instrument approach procedure (IAP) is a "series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight rules conditions from the beginning of the initial approach to a landing or to a point from which a landing may be made visually". A VOR/DME-C approach uses a VHF Omni-directional Range (VOR) signal from a navigational aid (NAVAID), and, associated distance measuring equipment (DME) to identify the aircraft position while on the procedure. The incident flight was vectored and subsequently cleared for the VOR DME-C approach from the initial approach fix (IAF) CEGAN.

The VOR DME-C standard instrument approach procedure (SIAP) published an altitude of 10,000 feet for the segment of the approach from the IAF CEGAN while the aircraft was on a 27-mile DME arc to the IAF BRKET. The published altitude from BRKET to the fix SERTE was 8,500 feet. The published altitude from SERTE to the fix GOLLD was 7,400 feet. The published altitude to the fix HURLO was 5,800 feet. Figure 4 illustrates the published approach chart for the MFR VOR/DMA-C approach. The instrument procedure listed the airport elevation as 1,335 feet and a descent angle of 6.91 degrees.

Figure 4 - The approach chart for the MFR VOR/DMA-C approach plate.

Minimum Vectoring Altitude

The FAA defines the MVA as "The lowest msl altitude at which an Instrument Flight Rules (IFR) aircraft may be vectored by a radar controller, except as otherwise authorized for radar approaches, departures, and missed approaches. The altitude meets IFR obstacle clearance criteria. It may be lower than the publis...