Finally, the potential physical effects of climate change, such as increased frequency and severity of storms, floods, fires, sea-level rise and other climate-related events, could affect our operations, infrastructure and financial results. Operational impacts, such as the canceling of flights, could result in loss of revenue. We could incur significant costs to improve the climate resiliency of our infrastructure and otherwise prepare for, respond to, and mitigate such physical effects of climate change. We are not able to accurately predict the materiality of any potential losses or costs associated with the physical effects of climate change. 

## We are subject to many forms of environmental and noise regulation and may incur substantial costs as a result. 

We are subject to a number of increasingly stringent federal, state, local and foreign laws, regulations and ordinances relating to the protection of the environment and noise reduction, including those relating to emissions to the air, discharges to surface and subsurface waters, safe drinking water, and the management of hazardous substances, oils and waste materials. Compliance with environmental laws and regulations can require significant expenditures, and violations can lead to significant fines and penalties. 

We are also subject to other environmental laws and regulations, including those that require us to investigate and remediate soil or groundwater to meet certain remediation standards. Under federal law, generators of waste materials, and current and former owners or operators of facilities, can be subject to liability for investigation and remediation costs at locations that have been identified as requiring response actions. Liability under these laws may be strict, joint and several, meaning that we could be liable for the costs of cleaning up environmental contamination regardless of fault or the amount of waste directly attributable to us. We have liability for investigation and remediation costs at various sites, although such costs currently are not expected to have a material adverse effect on our business. 

We have various leases and agreements with respect to real property, tanks and pipelines with airports and other operators. Under these leases and agreements, we have agreed to indemnify the lessor or operator against environmental liabilities associated with the real property or operations described under the agreement, even in certain cases where we are not the party responsible for the initial event that caused the environmental damage. We also participate in leases with other airlines in fuel consortiums and fuel committees at airports, and such indemnities are generally joint and several among the participating airlines. 

Governmental authorities in several U.S. and foreign cities are also considering, or have already implemented, aircraft noise reduction programs, including the imposition of nighttime curfews and limitations on daytime take offs and landings. We have been able to accommodate local noise restrictions imposed to date, but our operations could be adversely affected if locally-imposed regulations become more restrictive or widespread. 

## We depend on a limited number of suppliers for aircraft, aircraft engines and parts. 

We depend on a limited number of suppliers for aircraft, aircraft engines and many aircraft and engine parts. For example, under our current fleet plan, by the end of 2020 all of our mainline aircraft will have been manufactured by either Airbus or Boeing and all of our regional aircraft will have been manufactured by either Bombardier or Embraer. Further, our supplier base continues to consolidate as evidenced by the recent acquisition of Rockwell Collins by United Technologies, the recent transactions involving Airbus and Bombardier and the pending transactions involving Boeing and Embraer, and Bombardier and Mitsubishi. Due to the limited number of these suppliers, we are vulnerable to any problems associated with the performance of their obligation to supply key aircraft, parts and engines, including design defects, mechanical problems, contractual performance by suppliers, adverse perception by the public that would result in customer avoidance of any of our aircraft or any action by the FAA or any other regulatory authority resulting in an inability to operate our aircraft, even temporarily. In particular, in March 2019, the FAA ordered the grounding of all Boeing 737 MAX aircraft, which remains in place as of the date of this report. 

## Delays in scheduled aircraft deliveries or other loss of anticipated fleet capacity, and failure of new aircraft to perform as expected, may adversely impact our business, results of operations and financial condition. 

The success of our business depends on, among other things, effectively managing the number and types of aircraft we operate. If, for any reason, we are unable to accept or secure deliveries of new aircraft on contractually scheduled delivery dates, this could have negative impacts on our business, results of operations and financial condition. Our failure to integrate newly purchased aircraft into our fleet as planned might require us to seek extensions of the terms for some leased aircraft or otherwise delay the exit of certain aircraft from our fleet. Such unanticipated extensions or delays may require us to operate existing aircraft beyond the point at which it is economically optimal to retire them, resulting in increased maintenance costs, or reductions to our schedule, thereby reducing revenues. If new aircraft orders are not filled on a timely basis, we could face higher financing and operating costs than planned. In addition, if the aircraft we 

