Date: 201504
Local time of day: 1201-1800
Location: SDL.Airport, AZ
Flight conditions: VMC
Weather elements / visibility: 8
Light: Daylight
Aircraft: Gulfstream V / G500 / G550
Operator: Fractional
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class D SDL
ATC / advisory: Tower SDL
Reporter organization: Fractional
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Training / Qualification; Situational Awareness
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Automation Aircraft Terrain Warning; Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: We set up and briefed a visual approach with a stable 3.1 degree VNAV glidepath as reference after being cleared for a straight in visual approach to runway 21. We discussed and agreed to descend between two peaks as the approach proceeded. My excellent First Officer (FO) asked if we were sufficiently separated from the left hand peak; and I said yes. As we passed between the peaks on the stable descent; he expressed worries about our clearance on the left; and I said we have plenty of room; verified by my view from the left seat. Then the GPWS warned about terrain; and the FO wanted me to turn right to clear. I felt this would destabilize the approach which was proceeding just fine in my opinion; and we continued and landed.  We were navigating with visual reference to the hills; and the approach was totally stable.The FO and I need to find out if we are constrained by GPWS terrain warnings when we are navigating and descending visually. I feel it was a perfectly normal; stable and reasonable visual approach; and my FO; one of my favorite people to fly with; feels GPWS warnings about terrain require a responsive maneuver; even in good visual conditions. If I am wrong; I want to know. And I will cheerfully apologize to my FO; who is an excellent pilot.


Second narrative: We were on a STAR coming from the north of the SDL airport. The Phoenix approach controller began vectoring us off the STAR at approximately 20 miles north of the airport and descending us to 6000 FT MSL. We had the airport in sight and the Captain who was the pilot flying (PF) asked me to request a visual approach; which I did. Once we were cleared for the visual approach he began configuring the airplane for landing and descending out of 6000 FT. As we were approaching I noticed that there were two peaks (left peak being higher) just south of our position or north of the intended landing runway which was RWY 21. As we continue to approach straight in to the runway and descending I made it clear to the PF that I thought that he should come right in order to avoid the highest peak to our left. He mentioned that he was visual and that he was clear of the mountain. However; I felt differently and continue to voice my concern and aggressively asked him to come right to avoid the peak. At that time I also noticed that the highest terrain displayed on my MFD was 4200 FT and I asked him to stop descending as I saw that he was going through 4500 FT. We continue to approach between the two peaks and at this time he was hand flying the airplane and the speed was dropping off and he was complaining about the autothrottles not working and I was getting extremely concerned about the terrain and continue to ask for a right turn away from the peak. The inevitable happened and the GPWS started screaming; at first we got the 'caution terrain' and then we got the red caution 'Terrain Pull Up' I immediately commanded that he execute the maneuver and pull up but he refused to do it. I assertively asked for the controls but he wouldn't relinquish the controls. I fought to pull on the nose and push on the throttles but he was fighting me and would not remove his hands from the controls. I'm not sure how we got through it but shortly after we fought for the controls which was brief the GPWS stopped yelling at us and the terrain was behind us. I let go of the controls and he continue to land the airplane uneventfully. The passengers deplaned and I noticed the Lead talking to the Captian. I asked our flight attendant if he had noticed anything unusual and he said 'oh yeah' and so did the passengers as they made a mention of it. I have been flying for [company] for almost 10 years and I have never been this scared before.


Synopsis: Gulfstream V flight crew reported receiving a GPWS 'Terrain; Pull Up' warning on a visual approach to SDL; prompting the FO to command a go-around; but the Captain decided to continue.