Item No. 7a Supp 
Meeting Date: July 25, 2017
Revised July 27, 2017 (see slide 20)
Flight Corridor Safety Program
Sites P-4 and P-5
Briefing

1

Why Obstruction Removal? 
FAA regulations and WA State law require
airports to identify and remove obstructions
to navigable airspace 
Obstruction removal ensures safe operation
of aircraft 
Airports around the country manage similar
programs to protect the safety of the flying
public 

Safety of Flight 
2

Example of Flight Corridor Surfaces 


Protect Flight Corridor 
3

How the Program Ensures Safe
Operation of Aircraft 
Equipment Failure 
Weather 
Pilot Error 
Certification Compliance 
FAA Safety Regulations 
Vegetation Management 
Safety of Flight 
4

What are Obstructions? 
At Sea-Tac Airport  Primarily trees 
Existing Obstruction  Obstructions currently
penetrating flight surfaces 
Potential Obstruction  Obstructions that are
within 0-6' of penetrating flight surfaces 
Understory Vegetation  Non-obstruction
vegetation consisting of smaller trees and
shrubs growing beneath large trees
(obstructions) 
Vegetation Management 
5

Multi-year Program 
2016  2017: Port-Owned Property 
2017  2018 : Publicly-Owned Property 
Includes WSDOT, Seattle Public Utilities, Highline Public School
District and possible City right-of-way in the cities of Burien, Des
Moines, and SeaTac 
2018  2019: Residential & Commercial Property 
66 known residential properties 
9 known commercial properties 
On-going Vegetation Management 
6

Community Engagement 
2016:
Open House (April) 
Open House and Community Meeting (November) 
2017: 
Open House (February) 
Open House and Community Meeting on sites P4-5
(June) 
June 1 Open House for Sites P4 and P5 
7

Overview of Port Sites 


8

Port Property Update 
All obstructions have been removed from approved
Port Property (except P-4 & P-5) 
Replanting trees has occurred on Port property
(except P-1, P-4 & P-5) 
On-going irrigation throughout the summer as-
needed to increase plant
survivability/establishment 
On-going maintenance of invasive species to
increase plant survivability/establishment 
Additional shrubs to be planted in October, 2017 
Current status 
9

Sites P-4 and P-5 Update 
As directed by the Port Commission, Port staff
undertook additional community engagement
before determining the removal and replanting
approach on Sites P-4 and P-5 
Both sites contain a high number of large
conifers 
Both sites nearby to residential properties 

Re-assess the removal and replanting approach for P-4 and P-5 
10

Sites P-4 and P-5 Update 


Sites P-4 and P-5 
11

Sites P-4 and P-5 Update 
Port Removal and Replanting  What We Heard from the
Objectives                Public 
Eliminate obstructions          Stagger the tree removal to
Minimize environmental impacts     allow younger trees to mature 
Restore a diverse native forest     Protect and prioritize conifers 
community                Remove invasive species 
Maintain a barrier between sites   Maintain a barrier between sites
& adjacent neighborhoods         & adjacent neighborhoods 

Objectives and Public Input 
12

Removal Alternatives for P-4 & P-5 
Alternative 1 
Removal of Existing Obstructions, Potential Obstructions and Understory 
Alternative 2 
Removal of Existing Obstructions and Potential Obstructions 
Alternative 3 (Public favored) 
Removal of Existing Obstructions Only 
(Protect Potential Obstructions and Understory) 
Alternative 4 
Phased Removal of Existing Obstructions, Potential Obstructions and Understory 

Four Removal Alternatives 
13

Recommended Removal Approach 
Alternative 3: Removal of Existing Obstructions (Public
favored) 
- Protect Potential Obstructions and Understory 
Advantages                        Disadvantages 
Sites are obstruction-free for 5 years        Site reentered every 5 years after
30 to 40 tall conifers preserved for 5         to remove obstructions as they
years                               occur 
Phased plant reestablishment            Repeated disturbance to the site
Preserves saplings, shrubs and            may reduce success of replanting 
vegetation to the extent feasible.         Limited removal of invasive
species 
Recommend Removing Existing Obstructions 
14

Replanting Options P-4 & P-5 
Option 1 
Re-establish a Low-Growing Forest Onsite 
Option 2 
Re-establish a Low-Growing Forest Onsite with a Vegetation Barrier 
Option 3 
Replace Trees Onsite and Create a Tall-growing Forest Nearby with Vegetation
Barrier 
Option 4 (Community proposed) 
Combine Options 2 and 3 

Four Replanting Alternatives 
15

Recommended Replanting Approach 
Replace Trees Onsite, Create a Tall-growing Forest Nearby and Provide a
Vegetation Barrier adjacent to residential properties 





16

Recommended Replanting Approach 
Option 4: Replace Trees Onsite and Create a Tall-growing Forest
Nearby with Vegetation Barrier (Public favored) 
- Replant on-site over time as-needed to establish a low-growing forest 
- Replant in off-site location with tall conifers 
- Provide vegetation barrier adjacent to residential properties and road frontage 
Advantages                       Disadvantages 
Large containers allow trees to mature faster   Longer Period to Re-establish a
Prioritizes replanting of conifers             Low-Growing Forest Onsite 
Removes invasive vegetation 
Vegetation barrier for adjacent residences 
Tall-growing trees 
Recommend Replanting On-site, Off-site and Provide a Vegetation Barrier 
17

Next Steps 
Phase 1 
Develop Removal and Replanting Design
Documents 
Negotiate Change Order with the Contractor 
Begin Removal and Replanting Q3  2017 
Phase 2 and 3 
Initiate Environmental Evaluation Fall 2017 

Phase 1 Existing Obstructions and Phase 2 and 3 Planning 
18

Questions? 


19

Recommended Replanting Approach 
Replace Trees Onsite and Create a Tall-growing Forest Nearby 


OFFSITE 

SITE P-5 
SITE P-4                                20