PA-44 instructor reported an near midair collision returning from practice area flying the authorize...

Narrative:

[My student and I] were heading back to mesa gateway from the south east practice area through a well-known entry point the gap. The gap is used to funnel traffic between two peaks of the san tan mountains. I was at three thousand five hundred the authorized altitude for this arrival. There were multiple planes headed for the gap at this time; as I was about to make my final call on the practice area frequency I get a traffic alert on the tis (traffic information service) page telling me there was traffic directly to my right same altitude within a distance of approximately half a mile. I couldn't locate the traffic and decided it was best to take action and I began a climbing turn out to the left. At the same time there was [a training] aircraft approximately a mile behind my aircraft descending from four thousand five hundred down to the authorized altitude of three thousand five hundred. I did not know that this aircraft was that close to me nor that he was descending down on to my aircraft. I continued my left turn and crossed paths with this aircraft. We avoided each other and continued back into the gap and both aircraft arrived at mesa gateway safely. I was not aware that [the other aircraft] descends into the gap as the LOA with gateway tower states that aircraft should already be established at three thousand five hundred when entering the gap. That is why I choose to climb.

Original NASA ASRS Text

Title: PA-44 Instructor reported an NMAC returning from practice area flying the authorized arrival airport entry point.

Narrative: [My student and I] were heading back to Mesa gateway from the south east practice area through a well-known entry point the GAP. The GAP is used to funnel traffic between two peaks of the San Tan Mountains. I was at three thousand five hundred the authorized altitude for this arrival. There were multiple planes headed for the GAP at this time; as I was about to make my final call on the practice area frequency I get a traffic alert on the TIS (Traffic Information Service) page telling me there was traffic directly to my right same altitude within a distance of approximately half a mile. I couldn't locate the traffic and decided it was best to take action and I began a climbing turn out to the left. At the same time there was [a training] aircraft approximately a mile behind my aircraft descending from four thousand five hundred down to the authorized altitude of three thousand five hundred. I did not know that this aircraft was that close to me nor that he was descending down on to my aircraft. I continued my left turn and crossed paths with this aircraft. We avoided each other and continued back into the GAP and both aircraft arrived at Mesa gateway safely. I was not aware that [the other aircraft] descends into the GAP as the LOA with gateway tower states that aircraft should already be established at three thousand five hundred when entering the GAP. That is why I choose to climb.

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.

Attributes
ACN	1537049
Time
Date	201804
Local Time Of Day	0601-1200
Place
Locale Reference	IWA.Airport
State Reference	AZ
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	PA-44 Seminole/Turbo Seminole
Operating Under FAR Part	Part 91
Flight Phase	Descent
Flight Plan	None
Person 1
Qualification	Flight Crew Instrument Flight Crew Flight Instructor Flight Crew Commercial Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 198 Flight Crew Total 468 Flight Crew Type 175
Events
Anomaly	Conflict NMAC Deviation - Procedural Published Material / Policy
Miss Distance	Horizontal 500 Vertical 300

PA-44 instructor reported an near midair collision returning from practice area flying the authorized arrival airport entry point.